3321 lines
222 KiB
Plaintext
3321 lines
222 KiB
Plaintext
QUASARS, REDSHIFTS AND CONTROVERSIES
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QUASARS, REDSHIFTS, AND CONTROVERSIES
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Halton Arp
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Interstellar Media 2153 Russell Street Berkeley, CA 94705
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Interstellar Media
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2153 Russell Street Berkeley, CA 94705
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Copyright © 1987 by Halton Arp
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Reproduction or translation of any part of this work beyond the limits of Sections 108 or 108 of the 1976 United States Copyright Act without the permission of the copyright owner is unlawful. Requests for permission or further information should be addressed to: Permissions Department, Interstellar Media, 2153 Russell Street, Berkeley, CA 94705
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Library of Congress Catalog Card Number 87-080290
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ISBN 0-941325-00-8 Printed in the United States of America
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10 9 8 7 6 5 4 3 2 1
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TABLE OF CONTENTS
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Introduction
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1
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1 Distances of Quasars
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7
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2 The Battle Over Statistics
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17
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3 Galaxies Visibly Connected to Quasars
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31
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4 Certain Galaxies with Many Quasars
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47
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5 Distribution of Quasars in Space
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63
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6 Galaxies with Excess Redshift
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81
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7 Small Excess Redshifts, the Local Group of
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Galaxies, and Quantization of Redshifts
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107
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8 Correcting Intrinsic Redshifts and Identifying
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Hydrogen Clouds Within Nearby Groups of
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Galaxies
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115
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9 Ejection from Galaxies
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133
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10 The Sociology of the Controversy
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165
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11 Interpretations
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173
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Glossary
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187
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Index
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193
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PREFACE
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The purpose of this book is to present important information about the nature of the universe in which we live. Knowledge of the laws of nature offers humankind the only chance of survival in a changing environment. It endows us with the power to achieve whatever we consider our most desirable evolutionary goals. Perhaps most of all, the search for knowledge gives expression to a basic curiosity which appears to be the salient defining characteristic of human beings.
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The information about the physical universe that this book tries to convey is highly controversial. Since I believe that the facts are true and important, and since I have firsthand knowledge of the observations, I have undertaken to present the subject in the following book. Actually, this offers the only possibility of discussing this subject in a meaningful way at this time. The reasons for this are the following:
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First, the antecedent observations have been published over a span of twenty years in various technical, astronomical journals. In order to construct a coherent picture, these reports need now to be drawn together and related to each other. In the past, it has al-
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ways been possible to criticize or ignore individual discoveries and avoid the weight of accumulated evidence which a minority of astronomers have felt requires a drastic change in current assumptions about the universe. This book presents an integrated picture of this evidence which it is hoped will be compelling enough to establish the necessity for a new and large step forward in astronomical concepts.
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Secondly, there have recently been attempts by a few people in the field to suppress new results that disagree with their particular viewpoint. Telescope time needed to follow up discoveries in these directions has been denied. Research reports to journals have been rejected or modified by referees committed to the status quo. It is clear that when scientific results are prevented from appearing or being discussed in standard journals, the only alternative is to publish a book. Then no one who is interested is denied the opportunity of reading the evidence. Since many generalist readers are also interested in this subject, I have tried to write in a way that is comprehensible to nontechnical readers. Then no one, specialist or generalist, will be denied access to
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this new information if they wish to make use of it.
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I believe in order to gain the most fundamental knowledge of which we are capable it is necessary to continually and sincerely question our assumptions and test our theories. In a sense, the way we do science is more important than the exact results at any given moment. I have stated the results as correctly as I can in this book but one must always face the possibility that one's current understanding is
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more or less completely wrong. So, even if my thesis were mistaken—which I consider unlikely in view of the evidence—it may still have been valuable to have discussed how the process of astronomical discovery is actually conducted. The most important thing for us to recall may be, that the crucial quality of science is to encourage, not discourage, the testing of assumptions. That is the only ethic that will eventually start us on our way to a new and much deeper level of understanding.
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INTRODUCTION
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Redshifts and the Hubble Law
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In 1924, Edwin Hubble demonstrated that the small, hazy patches of light we see in the sky on a dark night—the galaxies—are really enormous islands of billions of stars, like our own Milky Way galaxy seen at a great distance. Study with large telescopes revealed that the fainter and smaller a galaxy appeared, the higher, in general, was its redshift. Redshift describes the fact that the characteristic lines in its spectrum due to hydrogen, calcium, and other elements appear at longer (redder) wavelengths than in a terrestrial laboratory. This effect was most simply attributed to a recession velocity of the emitting source—like the falling pitch of a receding train whistle. It was therefore concluded that the fainter and smaller the galaxy, the more distant it was, and the faster it was flying away from us. This is the velocity interpretation of the redshift-apparent brightness relation, the standard interpretation of the so-called Hubble law.
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About this time, Einstein was writing equations that attempted to describe the behavior of the entire universe, the totality of what exists. His equations pointed to its probable instability. Gravitation was either strong
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enough to be in the process of contracting the universe or too weak to prevent its expansion. In view of the extant conclusions about galaxy recession velocities, it was natural to interpret them as due to expansion of the universe. Extrapolating these velocities back to an origin in time gave rise to the concept of the universe being born in a primeval explosion, the so-called "big bang" cosmology.
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If this simple theory could explain all the observations, as it appeared to do for many years, then it would be what people strive for—an elegant solution. But it is my thesis in this book that from 1966 onward, observations began to accumulate that could not be explained by this conventional picture. Some extragalactic objects had to have redshifts which were not caused by velocity of recession.
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At the very least, it seemed that some modification had to be made to the current theory. The reaction against these discordant observations among some influential specialists was very strong: It was said that they "violated the known laws of physics" and therefore must be incorrect. Alas, it seems that in the intervening years the useful hy-
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Introduction
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pothesis had become enshrined dogma. Translated plainly, this dogma simply
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states: "At this golden moment in human history, we know all the important aspects of nature that we will ever know. In spite of a long record of fundamental revolutions in human thought, there are now no surprises, there is now an end to this history." This seems patently absurd. In fact, like most people, I would instinctively have a kind of temporal Copernican view that no arbitrary epoch is special. I believe that startling forward leaps in knowledge will continue to take place if the human race survives long enough. Nevertheless, I do not believe we can use extrapolation of past experience as a proof that this is taking place at any given moment. We must instead have concrete, specific evidence if a radical change is now needed. Therefore, my major goal in this book is to gather together all the proof existing at this moment, to show that there is massive, incontrovertible evidence for important phenomena and processes, perhaps even new forces or laws, which we cannot currently understand or explain.
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In order to force a change in the current paradigm, this book presents observations in detail. Unlike the current belief in the field that observations can be accepted or discarded according to whether they fit a theory, I submit that the observations in fact are the known laws of physics. It only is required for us to connect them together in some satisfactory way. In this process, however, the one thing we must guard against is the misinterpretation of chance occurrences. (Throughout history this has been a popular activity called superstition.) Therefore, in each of the many examples I discuss, I first try to establish that if the observation is not a chance occurrence, then a fundamental "law" has been broken. For example, if a high-redshift object occurs close by in space to a low-redshift object, then the redshift-distance relation has been violated. This reduces the proof to a yes
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or no decision. Either the closeness on the sky is an accidental projection of background and foreground objects, or there is a real physical proximity. We can then concentrate on determining how small the chance is that this observation is an accident. Even more important, we can determine whether there are other independent observations that support and confirm the reality of this result. Ultimately, each reader has to make his own decision whether the conventional law has been contradicted. But if we can gather enough different kinds of examples, as this book attempts to do, then perhaps we can achieve agreement that the phenomena are real. Then perhaps we can begin to discern repetitive patterns or similarities in the evidence that can be used to predict further examples and induce new hypotheses which could explain the phenomena. We will be underway into a new era.
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The first shock to conventional theory came with the advent of radio astronomy and the discovery of quasars. Therefore, we should first define the terms relating to these subjects.
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Radio Galaxies and Quasars
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The story of this new branch of astronomy begins for me on a bluff overlooking the ocean on the east coast of Australia, near the end of the Second World War. The operator of a radar station noticed a source of radio noise in the sky that rose 3 minutes and 56 seconds earlier each day. An astronomer immediately recognizes that this is just the amount the stars gain on the sun each day (sidereal time runs "faster" than solar time). This motion marked the source of radio noise as belonging to the realm of the stars and galaxies. That original observer, John Bolton, went on to help found the science of radio astronomy and direct some of the early radio observatories. The original radio source was in the southern constellation of Centaurus
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Introduction
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and became known as Cen A. Eventually, thousands upon thousands of cosmic radio sources were discovered. Many of them were eventually identified with disturbed or active galaxies like the galaxy responsible for Cen A. The radio emission is caused by charged particles moving in a magnetic field. Both the charging of the particles (their ionization) and their motion is a result of high temperatures and energetic events.
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These discoveries have required a fundamental change of concept about galaxies, a change that I believe has not yet been fully appreciated. It is no longer possible to view galaxies simply as relatively quiescent aggregates of stars, gas, and dust, all swirling in some majestic, ordered rotation about their center. Some are ripped asunder by huge explosions. Many have nuclei that vary strongly in brightness and intermittently eject quantities of matter outwards into space. In some ways, galaxies individually are reminiscent of the model of the universe as an exploding, or unfolding "cosmic egg." In my opinion, these new facts about the active nature of galaxies have not yet been integrated into a coherent picture of galaxy creation and evolution.
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But among radio sources that were identified with visible objects, an even more mysterious class than radio galaxies was found. These were the quasars. Optically they looked like point sources of light—like stars— hence their name "quasi-stellar" radio source, a term soon shortened to quasar. The first of these objects was identified by Allan Sandage and Thomas Matthews in 1963 in a collaboration between an optical and a radio astronomer. Then Maarten Schmidt, an astronomer at Caltech, found the key to the spectrum by showing the initially puzzling lines were those of familiar elements but shifted very far to the red. This was the shock. Why, when the highest redshifted galaxies known had maximum redshifts of 20 to 40 percent the velocity of light, did these stellar-looking objects suddenly appear with redshifts of 80 or 90 per-
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cent the velocity of light? It was briefly considered whether some other mechanism than velocity of recession could be responsible for quasar redshifts. For example, redshifting (which is equivalently a loss of energy of ~\ photon) might by caused by a very strong gravitational field. Such explanations were quickly discarded, however, and it was decided that quasars were the most luminous objects in the universe, seen at such great distances that the expansion of the universe was giving them the largest possible recession velocities.
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Difficulties were encountered almost immediately. In the first place, how could an object be so luminous? There was a problem of creating so much energy from known kinds of galaxies. Then, the calculated density of charged particles was so high in some quasars, that there was a problem of actually getting the photons, by which we see the objects, out from the interior. Then, very accurate positional measures by radio telescopes (very long base-line interferometry) revealed the astounding fact that some quasars appeared to be expanding with up to ten times the velocity of light. This was a flat-out violation of the known law of Einsteinian physics that the speed of light is a physical constant that cannot be exceeded in nature. Rather than move the quasars to lesser distances, which would give quite modest expansion velocities, the conventional theorists set up a small industry for rationalizations. They explained, by extremely complicated models, the faster-thanlight expansions as an illusion caused by very special, assumed conditions such as ejection toward the observer at nearly the speed of light. They, of course, ignored the direct evidence that the quasars were associated with galaxies which were much closer to us in space.
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When enough quasars were identified over the sky it became clear that anomalies also existed in the increase of their numbers with apparent faintness. For constant space
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Introduction
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density their numbers should have increased in proportion to the increased volumes enclosed at successively fainter apparent magnitudes. What was observed was completely different. This gave rise to another "gee whiz, isn't the universe wonderful" explanation. In this case, it was concluded that as we look out in space, and therefore back in time, we encounter a higher and higher density of quasars until suddenly—at a certain point—the quasars ceased to exist! In the present book, however, I do not debate whether this peculiar evolution of quasars is a priori improbable. I try to concentrate on the hard evidence of what they actually are and where they are located in space. In that process, we come again and again to observational evidence that redshift is not a good indicator of distances for quasars.
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Now the debate takes a curious turn. The conventional wisdom says quasars are just abnormal galaxies (superluminous, etc.) and that galaxies can only have redshifts caused by velocity. I say yes. I, myself, pointed out originally that quasars are physically continuous with galaxies. But a large body of evidence now exists showing that galaxies also can violate the redshift-distance relation. In fact, it is just the most peculiar galaxies, those most like the quasars, for which the most compelling evidence for nonvelocity redshifts exists.
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This has two consequences: First, it enormously strengthens the case that the redshiftdistance law can be broken. After all, it only requires one well-proven, discordant case of quasar or galaxy to establish that an additional cause of redshift—other than velocity—must be in operation. Because of the connection of quasars with galaxies we now have many, interlocking proofs of the phenomenon.
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But secondly it means that the mechanism for causing this nonvelocity shift must be capable of operating on an entire extended assemblage of stars, gas, and dust. This is
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much more difficult than finding a mechanism to operate on the more compact, more mysterious quasars.
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The advance in understanding required to explain these observations has been thereby considerably escalated and now represents a spectacularly exciting challenge. The stakes in the theory game have been sharply raised.
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The following book reflects the progression of evidence just discussed. The first five chapters deal with the anomalous evidence on quasars. The next three chapters deal with evidence for nonvelocity redshifts in galaxies. The final chapter combines this evidence and tries to explore the possible types of explanations which might account for the discordant data. Throughout the book, however, the reader will also be aware of many comments and anecdotes which bear on how the participants in the controversy have conducted the debate. The next-to-closing chapter deals with how I feel the acrimony arose in the debate and what it means for science.
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One of the reasons for this commentary is that the reader needs to be aware that many professional astronomers do not believe that there is any need to change the conventional theory. Some accomplished and noted professionals do believe important, fundamental changes are necessary. A number are waiting to make up their mind—or see what others decide. But a number of astronomers vehemently reject the observations or the conclusions from them which are presented in this book. There are only two possibilities: One is that the conventional wisdom is right and that the observations are meaningless accidents. The other possibility is that the present thrust of the observations is correct and that some radical changes will have to be made in current theory.
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This raises two questions for the reader: The first is, "What are the reasons which some astronomers give for disbelieving the evidence and conclusions of this book?" As
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Introduction
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to this question, I cannot possibly represent fairly the other side. Even if I could present it in an unbiased way, it would take an impossibly long time. The counterarguments to the evidence presented in this book, when they have been made in a few cases, are exceedingly complex and obscure and become hopelessly lost in technical detail. As Fred Hoyle has remarked, the establishment defends itself by "complicating everything to the point of incomprehensibility." I try to deal with valid, alternate possibilities as they arise, but the reader will either have to search out any original arguments from the references I give in the appendices to each chapter, or wait for a comprehensible rebuttal to this book to be published.
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The second question raised is: "Assuming for the moment that the evidence in this book is correct, why have many professional astronomers disbelieved it?" That is an exceedingly important question because it bears on how human beings discover and gain knowledge and avoid harmful, entrenched mythologies. That is the reason I have included personal anecdote and commentary in this book. In case the thesis of this book is correct, we want to know what the factors are
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that led to this long, implacable rejection of new knowledge, the wasted effort, and the retardation of progress. Inevitably these factors involve emotional, personal, and ethical questions. These are explosive subjects down through the history of mankind. I am sure emotions will be stirred as a result of my comments in this book.
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That I am willing to endure because I feel that the way in which research is conducted is one of the most crucial of mankind's activities. If the research is imaginative and accurate, and the human relations promote and protect this process, then the results will inevitably be worthwhile. If the process is biased, the practitioners too hostile or competitive for personal gain, or lacking in the crucial element of sportsmanship, then the results will inevitably be delayed and distorted.
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The reader will have to make up his own mind on both questions, the correctness of the thesis of this book and also the validity of the comments on why some people tried to reject and suppress the results. Each reader will have to make up his own mind on these two questions, as in most important matters in life, on the basis of the evidence he has seen or heard.
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Introduction
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DISTANCES l OF QUASARS
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The opposite page shows a photograph of knowledge toward the end of this book, but three quasars closely grouped around a first, let us just follow for a while the thread of
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large galaxy. The chance of these three qua- one particular story, the history of the claimed
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sars accidentally falling so close to a galaxy is association of quasars with galaxies.
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between 10"5 and 10~7, that is about one
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In 1966 while checking galaxies in my
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chance in a million. This is an enormously in- newly completed Atlas 0/ Peculiar Galaxies, I
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teresting observation because the quasars, noticed that radio sources, including some
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with high redshifts, are conventionally sup- quasars, fell close to, and aligned across, some
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posed to be far behind, and unrelated to the of the particularly disturbed galaxies. Quasars
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galaxy which has a much lower redshift. Nev- had been just discovered in 1963 and already
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ertheless, there was an attempt to suppress were being hailed as the most distant objects
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the discovery and observation of these qua- visible in the universe. If they were associated
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sars. When finally submitted to the Astrophys- with relatively nearby galaxies, such as in the
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iced Journal, publication was held up nearly Atlas, however, they would themselves have
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IV2 years. An anonymous referee stated, to be relatively nearby. Some explanation for
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"The probability arguments are completely their high redshifts would have to be found
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spurious."
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other than expansion of the universe at large
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What is the truth about this matter? Are distances. In March 1966, I gave the evi-
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the quasars related to the galaxy or not? And dence for these closer quasar distances in a
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why the emotion, intrigues, and deadly pro- colloquium at Caltech. I was told that one of
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fessional combat which the subject has in- the audience, later to become a vociferous op-
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spired for the last 20 years? To answer these ponent of the local hypothesis, had remarked
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questions, I believe, gives insight into the in a characteristically loud and over-
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state of knowledge in astronomy today and confident voice before the start of the confer-
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also illuminates the passions, prejudices, and ence, "Well, this will be the shot heard
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power relations in a modern science. We can around the room." In contrast, after the collo-
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explore the consequences of this for human quium, Fred Hoyle came up to the lectern
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Distances of Quasars 7
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and said, "Chip, we did not know about your results, but Geoffrey Burbidge and I have just submitted a paper which comes to the same conclusion, namely that quasars need not be the most distant objects, but could originate from nearby galaxies." But, in retrospect, it seems that the remark made that day, even before the observations were presented, signalled the implacable opposition of those who had accepted the original assumptions about quasars.
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The first independent test of the newly found association between radio sources, quasars, and certain types of galaxies was published in Nature magazine in 1966 (see
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Figure 1-1. Three quasars close to the galaxy NGC1842. The chances are about one in a million o{ finding this association accidentally.
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Appendix for reference). It concluded that the chance of obtaining the observed associations between peculiar galaxies and radio sources arranged randomly on the sky was about 1 in 100. But curiously, the authors took the standpoint that since the chance of being accidental was only 1 in 100, that there was no need to accept the significance of the association and test further the current assumptions. This attitude is distilled into the aphorism, "In order to make extraordinary changes in accepted scientific assumptions, one must have extraordinary observational evidence." Unfortunately, we will see that experience suggests that what this expression has come to mean in
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8 Distances of Quasars
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practice is: "In order to make basic changes in conventional assumptions, there is no evidence which is extraordinary enough".
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Naturally, this last attitude cuts the very foundation from under science. It will be of great importance for us to see, in the following pages, whether the evidence really is strong enough, and if it is, whether extragalactic astronomy has a hope of once again becoming a science.
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Quasars Associated with Galaxies
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In the years since 1966 some few astronomers produced many investigations that purported to demonstrate the association of quasars with low-redshift galaxies at high levels of significance. A few papers appeared attacking these conclusions and much private opinion was circulated that the associations were meaningless accidents. The reaction of the rest of the field seems to have been not to ask which of this published evidence was correct, but only to fall back on mutually spoken reassurances that the association was not accepted. Among the parade of papers demonstrating association, however, one particularly startling result emerged in 1979, namely that there were three quasars projected near the edge of the spiral galaxy NGC 1073. This was the first example of multiple quasars very close to galaxies, which, of course, would be very much less likely to occur by chance than single quasars close to galaxies. Figure 1-2 shows this very beautiful barred spiral with the quasars measured by myself and Jack Sulentic marked by arrows. Ironically, the galaxy was originally photographed by Hubble in 1950, and is featured in the Hubble Adas of Galaxies. This situation enabled me to make the pointed joke to my friend Allan Sandage, the author of that Atlas, and the co-discoverer of the first quasar, that his catalog of nearby galaxies seemed to contain many images of quasars well before they were discovered.
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The probability that three quasars would
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be observed by chance so close to NGC 1073 is about 2 x 10~5 or about 1 chance in 50,000. But NGC 1073 appears so large and bright that it is one of only 176 galaxies in the Hubble Atlas and one of only 1246 galaxies in the Shapky-Ames Catalog of Bright Galaxies. Of course, the vast majority of these have never been searched for the presence of nearby quasars. It was only by curiosity after a small radio source was discovered near the galaxy that I looked for other quasars nearby and found a total of three close to NGC 1073. Therefore, the previous prediction that quasars fell close to nearby galaxies had been confirmed with an extremely high probability of significance by this system. Even if no more cases like this were found among bright galaxies, it would still be a significant confirmation of the hypothesis that some low redshift galaxies have associated quasars.
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Usually in science one would expect an observation such as this to lead to the acceptance of the predicting hypothesis. In this case, the reality of the quasars was checked by some Caltech astronomers at Mt. Palomar Observatory, who refused to publish their confirmation and ignored the result. Confirmation was eventually published by the University of California astronomers E. Margaret Burbidge, V.T. Junkkarinen, and A.T. Koski. What the observation, and others like it, did lead to was a written warning from the allocation committee for Palomar telescope time threatening to cut my telescope time unless I refrained from such observations. In 1984, my observing time at Palomar was terminated.
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But the quasars sit there, apparently in the outer arms of NGC 1073. From where did they originate? What can we learn about the nature of these mysteriously redshifted sources of energy if they indeed are intermingled in the filaments of gas and young stars in this spiral galaxy? The most direct way to answer these questions, as well as to confirm the reality of the physical association, was to find further examples of such associations.
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Distances of Quasars
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It was helpful, therefore, when about the same time that the three quasars in the edge of NGC 1073 were being discovered, a pair of quasars turned up very close to the spiral galaxy NGC 622. The chance of finding two quasars this close to a galaxy is less than 4 x 10"1 or less than 2 x 10~5 if one takes into account that the second quasar is quite bright). I discovered this system during the inspection of plates that registered ultraviolet objects over about 100 square degrees of sky. There should be from 10 to 50 galaxies as bright as NGC 622 in the region searched. Therefore, this was another very significant confirma-
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Figure 1-2. Three quasars near spiral arms of the galaxy N G C 1073. Quasars discovered by Arp and Sulentic.
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tion. But the especially significant aspect of the NGC 622 configuration was a filament of material that came out of the galaxy and reached to the quasar, B1.
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Quasars Ejected from Galaxies
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This luminous connection is shown in Figure 1-3. It appears similar to a spiral arm of the galaxy except that it does not curve around as the edge of the galaxy does. Instead it comes straight out to end on what looks like an H II (gaseous emission) region. Right next to this knot is the quasar. The point is
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10 Distances of Quasars
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aw*-.- .:
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_.
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•
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Figure 1-3. Two quasars improbably close to the galaxy NCG 622. The fainter, higher-redshi/t quasar Bl lies near the end of a straight /ila• ment emerging from the galaxy.
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that the chances of this exceedingly unusual spiral arm ending almost exactly at the position of the quasar by accident is vanishingly small unless it is physically related. It also suggests ejection from the galaxy as the explanation for origin of the quasar. From the initial discovery of alignment of quasars across disturbed galaxies, the similarity to radio sources whose alignment is caused by ejection from the nucleus suggested an ejection origin for the quasars as well. The implication has always been that the quasars are ejected from the nucleus of the associated galaxy. We will see in coming chapters continuing and inter-
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locking evidence for ejection of material from galaxies. Second only to the question of origin of nonvelocity redshift, the ejection of material seems to be the most significant puzzle related to galaxies. Ejection from the nuclei of active galaxies raises the question of whether conditions in that innermost center involve the normal terrestrial physics that we know about. Could the strangeness of quasars be related to the very different nature of their material if they originated in active galactic nuclei?
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The quasar/galaxy associations shown in Figures 1-2 and 1-3 of the preceding pages
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Distances of Quasars 11
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Figure 1-4. Two quasars are seen projected very dose together near edge of N G C 470. Photograph try Allan Sandage. Note material in edge of galaxy apparently associated with quasars.
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were announced at the Texas Symposium on Relativistic Astrophysics in Munich in December 1978. This review paper presented evidence from systematic searches around a few dozen galaxies in selected regions of the sky. It was shown that a number of companion galaxies to spirals (apparently the most active kinds of galaxies) had single quasars close by to them with a probability of chance association, for the whole sample of only 10"* to 10~14. This was, of course, in addition to the highly significant confirmation of multiple quasars associated with galaxies which was already discussed here in relation to Figures 1-2 and 1-3.
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Most of the participants in the Texas Symposium were impressed by the results. But riding back to the hotel in the bus, I recall that in the deep seats immediately in front of me were Walter Sullivan, science writer for
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the New York Times and the most prominent quasar researcher of the day. The latter was explaining to Sullivan, with great patience and kindness, how all the apparent associations were accidental and how the quasars could not be local. To the credit of Sullivan, the stories on the associations did appear in the Times and similar evidence was also later reported in the Times over the years. But, the quietly spoken opinion of the astronomical authority was to prevail over the published evidence within his inner circle of science.
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The sharp and lethal battle which came in 1983 about the statistics of quasars near galaxies will be the subject of the next chapter. But first let us bring the story of multiple quasar associations up to date by reporting a more recent discovery. This is shown in Figure 1-4. The bright, spiral galaxy from the
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12 Distances of Quasars
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Shipley-Ames Catalog of Bright Galaxies, N G C 470, is shown to have two newly discovered quasars in the edge of its disk. The probability of finding two quasars like the fainter one this close to a given point in the sky is about 2 x 10"4. Since one quasar is considerably brighter, and therefore less common, the probability of finding the actual quasars is even smaller. This discovery comes from an area in which about five galaxies this bright were present. Therefore, the total probability of finding this configuration by accident in that investigation was less than one in a thousand.
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It is interesting to note how my collaborators in this discovery computed the probability. Putting forward the hypothesis that this is what drew attention to the galaxy, they began by pretending the first quasar did not exist. Then they asked, what is the probability of finding only the second quasar this close to a galaxy? Since this probability is still quite
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small, they said, well, let's move it further away from the galaxy where it would still attract our attention but where it would be more probable to encounter by accident. They still obtained a significant improbability for their modified configuration but, of course, much less than the improbability of the actual association. I am quite pleased that they were willing to publish their computation in our paper because I think it furnishes a surprisingly vivid record of how, when astronomers of conventional belief have a choice between two possibilities, the more bias toward the current assumption they make, the more proper they feel the calculation is.
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Of course, the latest discovery is the strikingly close arrangement of three quasars around the galaxy shown in Figure 1-1. This object will be discussed further in later chapters.
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Table 1-1 summarizes the properties of those four systems in which we, so far, have
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Name
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GALAXY Redshift
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TABLE 1-1 Galaxies With Multiple Quasars
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QUASAR
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Name
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Dist.
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Mag.
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Red
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(arcsec)
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Shift
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Probability
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NGC 622
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0.018
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|
UB1
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71
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|
BSO1
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|
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|
73
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|
18.5
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|
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|
0.91
|
|
|
|
0.001
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|
20.2
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|
1.46
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|
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|
0.02
|
|
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|
NGC 470
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0.009
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|
68
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|
|
|
95
|
|
|
|
19.9
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|
|
|
1.88
|
|
|
|
0.015
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|
|
|
68D
|
|
|
|
95
|
|
|
|
18.2
|
|
|
|
1.53
|
|
|
|
0.002
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|
NGC 1073
|
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0.004
|
|
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|
NGC 3842
|
|
|
|
0.020
|
|
|
|
BSO1
|
|
|
|
104
|
|
|
|
BSO2
|
|
|
|
117
|
|
|
|
RSO
|
|
|
|
84
|
|
|
|
QSO1
|
|
|
|
73
|
|
|
|
QSO2
|
|
|
|
59
|
|
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|
QSO3
|
|
|
|
73
|
|
|
|
19.8
|
|
|
|
1.94
|
|
|
|
0.01
|
|
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|
18.9
|
|
|
|
0.60
|
|
|
|
0.006
|
|
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|
20.0
|
|
|
|
1.40
|
|
|
|
0.02
|
|
|
|
19.0
|
|
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|
0.34
|
|
|
|
0.003
|
|
|
|
19.0
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|
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|
0.95
|
|
|
|
0.002
|
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|
|
21.0
|
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2.20
|
|
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0.01
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Distances of Quasars 13
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found galaxies with multiple, apparently associated quasars. An estimate of the improbability of chance occurrence is given for each quasar. It is noticeable that the quasars have a tendency to be fainter for larger redshift. This will be discussed in later chapters where evidence is advanced that the high-redshift quasars (z=2) have the lowest intrinsic luminosity. It is also noticeable in Table 1-1 that certain preferred redshift values appear more frequently than one would expect by chance.
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Preferred Values of Redshift
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This observed property of quasars having certain preferred redshifts has an extraordinary history and followed a typical course in the field. Geoffrey Burbidge noticed early in the measurements of quasar redshifts that too many redshifts occurred too close to the value z=1.95. He argued vigorously for the reality of the effect but others put emphasis on the quasars of other redshifts which were observed and ridiculed the effect. There was a sort of heroic underground of analysis of quasar periodicities starting with Burbidge and Burbidge in 1967 and continued by a number of astronomers, particularly Karlsson in 1971, 1973, and 1977, Barnothy and Barnothy in 1976, and Depaquit, Pecker, and Vigier in 1984. They all more or less agreed if you looked at all quasars known, that preferred values of redshift were apparent.
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In the latest and most complete analysis those preferred values of redshift were:
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TABLE 1-2
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z (ALL QUASARS)
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z (NGC 1073)
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0.30
|
|
|
|
0.60
|
|
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0.60
|
|
|
|
0.96
|
|
|
|
1.41
|
|
|
|
1.40
|
|
|
|
1.96
|
|
|
|
1.94
|
|
|
|
As the small table above shows, the redshifts of the quasars belonging to NGC 1073 (Figure 1-2) average only 0.01 from three of the magic values. This is like a key fitting into a lock. But, of course, what is behind that locked door is terrifying to conventional astronomy.
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The three quasars around NGC 3842 (Figure 1-1) fit a pattern of slightly different periodicity, a period characteristic of a different group of quasars. These slight differences in period interval between groups of quasars confirm the main periodicity and at the same time confirm that each individual association of quasars is a physically related group in spite of their being composed of different redshifts. This result will be analyzed further in Chapter 5, where evidence for the reality of different groups of quasars in different regions of space will be presented. References and further comments on the past analyses of periodicities in redshifts of quasars are given at the end of the Appendix to this chapter.
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|
Summary
|
|
To summarize this initial chapter, I would emphasize that with the known densities with which quasars of different apparent brightness are distributed over the sky, one can compute what are the chances of finding by accident a quasar at a certain distance from a galaxy (see Appendix to this chapter). When this probability is low, finding a second or third quasar within this distance is the product of these two or three improbabilities, or very much lower. It is perhaps difficult to appreciate immediately just how unlikely it is to encounter quasars this close by chance, but when galaxies with two or three quasars as close as we have shown here are encountered one needs only a few cases to establish beyond doubt that the associations cannot be accidental.
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We should also note that the hypothesis that quasars fall closer to galaxies than would be expected by chance was made and demon-
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14 Distances of Quasars
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strated by the available evidence in 1966. Long before the writing of this book a number of investigations had confirmed this association. But the present chapter, which presents the latest evidence on just the multiple quasar associations alone, confirms with overwhelming significance the fact of the associations.
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|
The vast majority of galaxies remain to be investigated. It is clear that many of these will yield additional confirmations and give further valuable data on the properties of the
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quasars which would help us understand the real nature of their redshifts. The last few observational programs of this kind have now been blocked by the committees which have been appointed by most observatory directors to allocate telescope time. It is with a considerable sense of relief, however, that I can say that I think the observations have been suppressed too late. As I hope we can continue to demonstrate in this book—the observational proof of this extremely important phenomenon has already been gathered.
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Appendix to Chapter 1—Probabilities of Associations
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|
The basic quantity needed to compute the probability of a quasar falling within any given distance from a point on the sky is just the average density of that kind of quasar per unit area on the sky. For example, if a quasar of 20th apparent magnitude falls 60 arcsec away from a galaxy, we simply say that within this radius of a galaxy there is a circular area of 0.0009 square degrees. The average density of quasars from the brightest down to 20th apparent magnitude is about 6 to 10 per square degree. Therefore, the most generous probability, on average, for finding one of these quasars in our small circle is about 0.001 x 10 = 0.01, that is, a chance of about one in a hundred.
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|
The crucial quantity is the observed average density. The comparison of what various observers have measured for this quantity is given in Arp 1983, page 504 (see following list of references). Overall, the various densities measured agree fairly well, certainly to within 140%. For the kinds of quasars considered in these first few chapters this gives probabilities that cannot be significantly questioned. Of course, on the cosmological assumption, quasars of various redshifts must project on the sky rather uniformly. Therefore adherents of this viewpoint cannot object to taking an average background density, as observed, to compute probabilities of chance occurrences.
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|
Although quite smooth enough to compute average probabilities of association as done in the previous chapter, the cosmological assumption of uniform quasar background has led to some consternation for certain other kinds of quasars discussed in later chapters.
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|
Typically one astronomer will measure one kind of quasar in one direction and get either a large or small difference from previous measures. He will then argue that his measure is "the" correct answer and other observers were in error. He will seldom consider that the differences are real. This has led to some considerable gymnastics to try to avoid inhomogeneities of certain kinds of quasars in certain regions. A good example of this is in the 1981 reference below, which tries to rationalize a difference of more than a factor of 10 in bright apparent magnitude, high-redshift quasars in one direction in the sky. In another instance, noted below, differences in densities are dismissed as scale errors when in fact they are due to the use of continuum magnitude systems that exclude emission lines, being incorrectly compared to broad-band systems that include them.
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|
Some references which will amplify subjects discussed in this chapter are listed below with some comments.
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|
1967, Arp, H., Astrophysical Journal, 148, p. 321. This is the first detailed paper discussing associations between radio sources and peculiar galaxies.
|
|
1966, Lynden-Bell, D., Cannon, R. D., Penston, M. V, and Rothman, V. C. A., Nature. 211, p. 838. First tests of the above associations.
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|
1968, van der Laan, H., and Bash, F. N., Astrophysical Journal, 152, p. 621. 1968, Arpi H., Astrophysical Journal, 152, p. 633. •
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|
First paper critical of the associations and reply by Arp.
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|
1973, "The Redshift Controversy," ed. G. Field, W. A. Benjamin, Inc., Reading, Mass. Three points not widely known about this, a report of the only actual debate to take place on the subject, are: (1) I
|
|
tried to challenge the best-known quasar experts in the field at that time but none would accept; (2) after the debate had
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Distances of Quasars 15
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been arranged, the director of my observatory heard that it was going to take place and telephoned to try to stop it; (3) the profits from the sale of the book went to support the work of Section D, the astronomy section of the AAAS (American Association for the Advancement of Science) before which the debate was held. The book summarizes and discusses the main developments before 1972. 1979, Arp. H. and Sulentic, J. W., Astrophys. Journal, 229, p. 496.
|
|
This is the report of the three quasars closely spaced around the galaxy NGC 1073 (Fig. 1-2 here).
|
|
1980, Arp H., Annals of the New York Academy of Sciences, 336, p. 94. This is a review paper given at the Ninth Texas Symposium on Relativistic Astrophysics held in Munich in Dec.
|
|
1978. The paper summarizes the associations of quasars and galaxies to that date, reports the associations with NGC 622 and NGC 1073, and introduces the associations of quasars with the famous disturbed or exploding galaxy, M82.
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|
1981, Smith, M.G., "Investigating the Universe," ed. F. D. Kahn, D. Reidel Publishing Co., Dordrecht, Holland p. 151.
|
|
This article attempts to rationalize order-of-magnitude discrepancies in quasar densities in different directions and backward running Hubble relations as "selection effects." See articles below:
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|
1983, Arp, H., Nature, 302, p. 397. 1984, Arp, H., Astrophys. Journal, 285, p. 555.
|
|
These two articles discuss the evidence against excusing quasar groupings and redshift-apparent magnitude anomalies as selection effects.
|
|
1982, Veron, P. and Veron, M. P., Astron. and Astrophys., 105, p. 405. This paper dismisses discrepancies in quasar densities in different directions as "due to errors in magnitude scales
|
|
used." The paper below shows it failed to distinguish between continuum and broad-band magnitudes.
|
|
1983, Arp. H., Astrophys. Journal, 271, p. 479. On page 504 of this article the density of quasars on the sky is discussed, comparisons are made to values measured
|
|
by various observers, and different magnitude systems are discussed.
|
|
1984, Arp. H. and Gavazzi, G., Astron. and Astrophys., 139, p.240. Discussion of three quasars newly discovered around NGC 3842 as shown in this chapter in Figure 1-1 and Table 1.
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|
1984, Arp, H., Surdej, J., and Swings, J. P., Astron. and Astrophys., 138, p. 179. Discussion of two newly discovered quasars at the edge of NGC 470 as shown in this chapter in Figure 1-4 and Ta-
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|
ble 1.
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|
Periodicities in the observed quasar redshifts have been analyzed by a number of authors. The latest references, from which the earlier references may be gleaned are: 1984, Depaquit, S., Pecker, J.-C., and Vigier, J.-P., Astronomische Nachrichten, 305. p. 339. 1984, Box, T. C. and Roeder. R. C , Astronomy and Astrophysics, 134, p. 234.
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|
Note on Periodicities in Quasar Redshifts.
|
|
Periodicities in quasar redshifts have been found in all samples except one where the person who analyzed it truncated the sample in a particular way that removed the periodicities (see Depaquit et al. reference). Some authors have argued selection effects are responsible for the periodicities. This is clearly untrue because major emission lines can be seen with objective prism searches throughout the redshift range. Concentrations of redshifts close to z = 1 for optically selected quasars around companion galaxies and in dense groups of quasars prove that techniques of photographic discovery by ultraviolet excess are not significantly biased. Of course, quasars selected by their radio emission should not be biased in redshift at all. It is shown in Chapter 5 that all quasars tend to have certain rather discrete, permitted redshifts but that different groups have slightly different periods. It is the addition of these slightly shifted peaks from group to group which broadens the overall peaks as observed in the total quasar sample. The bottom line is that quasars have the astonishing property of occurring at certain preferred values of redshift, these values occurring with a definite period whose origin is a mystery at this moment.
|
|
The crucial discovery of periodicities in quasar redshifts was made by K. G. Karlsson. That discovery was that the redshift peaks fit a formula A log (1 + z) = const. As Table 2 in the preceding text shows, the observed redshift peaks for the average of all quasars fit the formula with const. = 0.089. Individual physical groups of quasars have slightly different constants (see Arp, review paper presented at JAU Symposium 124, Beijing, China, August 1986). Unfortunately, a possibility of which all young astronomers are aware occurred in the Karlsson case. This creative researcher was not employed in astronomy and subsequently went into medical science.
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16 Distances of Quasars
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THE BATTLE 2 OVER STATISTICS
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As mentioned in the first chapter, after 1966, a number of investigations built up the evidence that quasars were associated with nearby galaxies. One of the first systematic investigations of quasars over the sky was an analysis I published in 1970. I was still a faculty member at Caltech at the time, and I remember well the custom of astronomy luncheons at the Faculty Club every Friday. I would bring in new examples of quasars falling improbably close to galaxies and share these photographs with my colleagues. Finally, the consensus was communicated to me that they believed these to be specially selected cases and that as scientists they could only accept the effect if a full statistical test were performed on a complete sample. I thereupon took about six months away from normal activities, enlisted the aid of Fritz Bartlett, a radio astronomer, to program the large IBM computer which Caltech then relied upon, and proceeded to analyze the position of all the then-known 3CR quasars (Third Cambridge Catalog Revised Survey of Strong Radio Sources) with respect to all the galaxies listed in the ShapkyAmes Catalog of Bright Galaxies.
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|
Figure 2-1 shows the striking result of those computations. It shows how the separations on the sky between a set of radio quasars and cataloged galaxies steadily decreases as brighter and brighter galaxies are considered—that is, the association with these quasars is stronger as galaxies closer to us in space are considered. The powerful computer enabled many imaginary sets of random quasars to be generated and compared to the galaxies, and thus showed that it was only the real quasars which had this property of falling closer and closer to brighter and brighter galaxies.
|
|
I returned with excitement and anticipation to the Friday luncheon and explained what I had found out. There was a unanimous response
|
|
"Oh, no one believes statistics!" The paper containing these results was published in 1970 in the Astronomical Journal and little notice was taken of it. Eventually, in 1983, I utilized some of the clues developed in that paper to make the most recent and detailed proposals as to the location of quasars in space. These concepts are developed further in Chapter 5.
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The Battle Over Statistics 17
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1
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1
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1
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1
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i
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rr
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to '2° -
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-
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o
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RANDOM QUASARS
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|
LL
|
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|
o io° -
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-
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|
XUON
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< 8° -
|
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-
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u
|
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</)
|
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|
REAL QUASARS
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|
LU
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§ 6° -
|
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-
|
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on
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|
HI
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A0
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i
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9
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i
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i
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i
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i
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10
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11
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12
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13
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APPARENT MAGNITUDE OF GALAXY
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Figure 2-1. The mean separation of a set of radio emitting quasars from very bright galaxies. Adapted from Arj> (1970).
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|
But, other investigators were also developing evidence that quasars were associated with galaxies on the sky. In 1971, G. R. Burbidge, E. M. Burbidge, P. M. Solomon, and P. A. Strittmatter showed that among the quasars then known, those that fell very close on the sky to bright galaxies fell much closer than would be expected by chance. In a carefully worked-out statistical analysis, they showed that with even the few cases known from casual investigation, the chance that these closest coinicidences occurred accidentally was less than 5 x 10~3 or of the order of one in two hundred.
|
|
The result was never criticized in print. As usual, however, it was excoriated in private. One of the major techniques for dismissing such results was introduced about this time. The catch-phrase is known as "a posteriori statistics." Normal people may not find that so catchy. But the idea is rather simple: After any event has happened, the probability of it happening in that precise way can al-
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ways be computed to be vanishingly small. For example, if two people are photographed in the streets of a city of one million inhabitants, we would say that the chance of A being directly adjacent to B is one in a million. But in any random street scene there are perforce many A's next to unrelated B's. This is all quite evident from common sense. But what is also quite evident from common sense is, that if we continue to get photographs at different times and places of A next to B, we had better conclude some relationship exists between A and B. So far as the charge of "a posteriori statistics" which has been levelled at each new piece of quasar evidence is concerned, the association of quasars with galaxies was demonstrated in 1966. Each succeeding example has therefore been an additional confirmation of an "a priori" prediction. The dismissal of each of these on a case-by-case basis with the excuse of " posteriori statistics" has been, at best, poor science and, at worst, a tactic of evasion.
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18 The Battle Over Statistics
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30
|
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300
|
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3000
|
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30000
|
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REDSHIFT OF GALAXY (km/sec)
|
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Figure 2-2. Relation showing that the greater the distance of the galaxy from the observer, the smaller is the apparent separation of the associated quasar. From Arp (1983).
|
|
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|
G. R. Burbidge, S. L. O'Dell, and P. A. Strittmatter in a later paper in 1972 showed that quasars associated with more remote galaxies appeared closer to the galaxy of association, as if the whole partnership was viewed from a greater distance. This relation is very important because it is what we must expect if we view associations through a range of distances, some associations close by and some more distant. The relation was later strongly confirmed over a much larger range in distance of the central galaxy and with larger numbers of examples in a paper by Arp in 1983. This is shown here in Figure 2-2.
|
|
At first sight this result seems to contradict the previous result that quasars fall closer to brighter, more nearby galaxies. The key point to understand, however, is that nearby quasars are statistically close (closer, on the
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average, than one would expect by chance) to nearby galaxies and that more distant quasars are statistically close to more distant galaxies. But, the nearby associations can subtend a large angle on the sky and have rather large separations compared to the separations involved in more distant associations. The difficulty comes when people assume on the local hypothesis (quasars closer than their redshift distances) that all quasars are at the same distance and then try to analyze this mixture of quasars at different distances with galaxies at different distances. Naturally they get porridge. An example of this follows.
|
|
In 1980, a test analysis was made by one researcher of some quasars which had been found in sample areas of the sky by objective prism techniques. (The objective prism on a telescope enables the selection of objects
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The Battle Over Statistics 19
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which have strong emission lines in their spectrum—the stellar images among these are mostly quasars.) These objective prism quasars were analyzed to see how close on the sky they fell to NGC galaxies. (Perhaps indicative of the fast pace at which astronomy moves, the New General Catalog of Gahxies (NGC) by Caroline and William Herschel was completed by J. L. E. Dreyer in 1888.) The NGC contains over 7000 objects, most of which are fainter objects at medium to large distances. There are no accurate magnitude limits for this Catalog and in addition an inhomogeneous selection of objects was made. But the Arp paper in 1970 showed bright quasars to be generally associated with the brightest galaxies in the sky. Why did the later paper in 1980 try to associate quasars with more distant galaxies?
|
|
And, should it have been such a surprise when it reported no significant associations? Perhaps there is some clue to be had in reading carefully the words of the author as he coyly "suggests" that the "seemingly high frequency of quasar/galaxy pairs reported, primarily by Arp" may be due to "uncertainties" in the adopted quasar densities used and "it is this effect that makes many astronomers skeptical about the statistical significance of Arp's configurations."
|
|
The true state of affairs was illuminated a year later by the only young astronomer to have ever regularly dared to test the claims of the establishment. Jack Sulentic analyzed the quasars just discussed as having been claimed to disprove association with galaxies. He analyzed these same quasars and also additional samples, but this time with respect to the bright nearby galaxies with which they were supposed to be associated. He found consistent and significant quasar/galaxy associations in all the quasar samples! Moreover, he found the quasars associated with fainter galaxies fell closer to them on the sky as would be expected if these fainter galaxies were more distant.
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|
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|
All this poses an interesting question: Why, when the establishment believes so fiercely in the different distances of galaxies (as indicated by their different redshifts), do they always insist on testing the association of galaxies and quasars by assuming that all galaxies (bright and faint) are at the same distance from us?
|
|
We will see this obviously incorrect assumption used again and again in attempts to disprove the association of quasars and galaxies.
|
|
A. Quasars near Companion Galaxies
|
|
During these investigations of quasars associated with galaxies, it became apparent that a particularly favorable configuration existed when a large spiral had an associated companion galaxy. Strikingly closer to these companions than expected by chance were found quasars.
|
|
A representative selection of the cases is shown in Figure 2-3. One reason for this could be that the companion galaxies are younger and more active and tend to produce more quasars. But whatever the explanation may be, the associations furnish vivid evidence of quasars associated with much lower redshift galaxies.
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As this evidence built up, the opposition became more silent. I felt that one final test would enable a resolution of the question. Starting in 1978, I outlined a considerable section of the sky, defined beforehand what kinds of galaxies I was looking for quasars around, and started to make the observations. (The area of the sky sampled was defined by bright spirals with companions that were contained between the right ascensions of NGC 2460 and 3184.) For long nights on the Mt. Palomar 48-inch Schmidt telescope I photographed these areas in the sky in two colors in such a way as to be able to pick out the ultraviolet-excess, stellar-appearing objects which were the quasar candidates. I labori-
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20 The Battle Over Statistics
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ously scanned the plates for the candidates and struggled with the spectrograph on the 200-inch Mt. Palomar reflector to obtain their individual spectra so that I might know with certainty which were bona fide quasars.
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Finally, after three years, I had finished. From 34 predefined candidate galaxies, I had found 13 cases where the quasars fell so close that the chances were, in each individual case, only about 1 in 100 of being accidentally associated. To find 13 such cases out of a limited number of trials implied fantastic odds against being a chance occurrence. I calculated about 10"17 (one chance in a billion would be 10-9)
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The result was published in the Astrophysical journal. A month or so passed. Suddenly the storm broke. Two papers arrived, each denouncing the probability calculations. They had been sent to the Astrophysical Journal Letters for quick publication and copies had been sent on to me by the Journal as a customary notification of critical papers. Both papers took essentially the same tack, that because I had used a probability of about one in a hundred of being accidental as a criterion for being associated, all cases where the probability was even slightly greater should be excluded. They wound up in the ludicrous position that associations where the probability was 0.012 or 0.013 should be excluded from the calculation as not improbable. (Basing my original probability calculation on p < 0.015, instead of the rounded-off p — 0.011 used, would have raised my final probability of accidental association from p ~ 10"" to p = 7 x 10""). These papers also used scaled densities of faint quasars to calculate the probabilities of finding bright quasars, despite the fact that it was clear from the literature that these brighter quasars were much less common. They also assumed that areas had been searched for quasars that had not been searched. These papers, after extensive refereeing, were never published. What did the damage was a paper that used the same in-
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correct arguments which was published with extreme rapidity by a British journal, Monthly Notices of the Royal Astronomical Society.
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I first became aware of this paper when I received an unprecedented note from the editor of the main Astrophysical Journal. (The main Journal has a separate editor from the Letters section.) He mailed me a preprint of the paper which was to appear so quickly thereafter in the Monthly Notices. The note from the Ap. J. editor read essentially:
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"We received this from the author and are conveying this simply for your information."
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Professional ethics required that both the author and the Monthly Notices send this kind of preprint directly to me. But, since from that day forward, my papers had enormous difficulties appearing in the Astrophysical Journal, I eventually understood what was the probable reason for this highly unusual maneuver.
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There was a further effect of the Monthly Notices paper, however, which presented me with additional problems. Another astronomer from the British establishment, who had been in communication with the first, sent a note to the Astrophysical Journal Letters which was eventually published. It took a different, apparently more valid tack. It pointed out that when I computed the probability of finding a quasar of a certain brightness at a certain distance from a galaxy, that I should also take into account that I could find other quasars at different brightnesses and distances that could also have a low probability of chance occurrence. In other words, there was more than one way of obtaining a chanceoccurrence probability of about 1 in 100. That gave me a number of sleepless nights because I had to acknowledge that this appeared to be a flaw in my original thinking.
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After pondering the question deeply, I finally came to the conclusion that I had intuitively assumed that galaxies at a certain distance would possess quasars at a certain,
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The Battle Over Statistics 21
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figure 2-3. A representative set of examples of large spirals that have companion galaxies with apparently associated quasars. The arrows mark the quasars. See also N G C 5296/97 in following chapter (Fig. 3-6). None of these examples were used in the complete statistical analysis of the test area discussed in the text and shown in Figs. 2-4 through 2-6.
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characteristic separation from the galaxy and that other separations would not occur. Actually, this is just the relation shown in Figure 22. With considerable anxiety, I recalculated the probabilities in a completely different manner, taking into account explicitly instead of implicitly the distance of the central galaxy calculated from the conventional redshift criterion of its distance. I got the same improbability of association. I felt vastly relieved that my initial assumption had been correct.
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I encouraged publication of the paper that criticized this aspect of my previous probability calculation and accompanied it with a recalculation, by the different method, which confirmed my original results. Actually, the critical paper, even after making the most unrealistic and unfavorable assumptions, still derived an improbability of 10"' that the original result could be accidental. This was still enormously strong confirmation of my original result. But the whole point of that paper was suddenly contradicted by a note added in proof (unseen by me or any referee) that referred to the Monthly Notices paper as disproving my original result. So the whole scientific content of the exchange was defeated. Reading now the papers, from some distance in time, it is clear that this was a rather effective double-play between two authors. In order to eliminate what seemed to be the inescapably small probability of chance occurrence originally obtained, one claimed that part was due to a large factor of error due to one cause and the other a large factor of error from another cause—neither had to make a formal calculation from the actual data.
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An extensive recalculation on these data was later made by two other authors, E. J. Zuiderwijk and H. R. de Ruiter. It was reported in the Monthly Notices 1983 (see Appendix). With essentially the same precepts as the earlier authors, they found instead an association of quasars with the galaxies with an
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overall chance of only about 1 in 100 of being accidental. The reason that this still fell short of my original improbability is that they also ignored the fact that the galaxies with which the quasars are associated have varying distances from us. The absolutely key point is that my original calculation used a simple way of taking into account the different distances from us of the galaxies around which the quasars were found. To ignore this elementary piece of astronomy in which everyone believes leads to a strong dilution of the effect by looking in areas where quasars are not expected to be found and ignoring areas where they are. The nub of the matter is the following: When testing the null hypothesis, the assumption that the quasars are not associated, the last two authors find evidence for association. The burning question then becomes, why not test the hypothesis that they are associated, taking into account the varying distance of the galaxies? Why not repeat the test which gave the original, overwhelmingly significant association with the galaxies?
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Of course, when two sides differ so sharply over calculations performed on the same data, one side must be wrong. If my side is wrong, I have to wonder whether I got the wrong answer because I wanted very much a certain result and this desire prejudiced my judgment on how to make the calculation. The other side would have to face the same question. Perhaps this is what is preventing the calculation from being pressed to the decision that it is certainly capable of.
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Finally, in 1983, a paper by myself was published in the Astrophysical Journal giving the final data on the observed fields and reanalyzing the statistics. Figure 2-4 here is from that paper and shows how the quasars concentrate between about 7 to 20 kpc radius around the particular galaxies that were sampled in that investigation. The average background density of quasars could not conceivably contribute significantly to the
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24 The Battle Over Statistics
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10
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on 8 /
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RADIAL DISTANCE FROM GALAXY (kpc)
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figure 2-4. Numbers of quasars found as a function of radius around companion galaxies in Arp's 1983 study. Expected average background counts are shown Iry the dashed line.
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observed numbers in the small area on the sky in which these quasars were found. In fact, the density of quasars at these radial distances from their associated galaxies (in this investigation the investigated galaxies were all companion galaxies to larger galaxies) exceeded by more than 20 times the measured density of these kinds of quasars away from such galaxies. This result appears in Figure 2-5, where the error bars on the determinations from quasars of various apparent brightness class are also shown. All three magnitude classes of quasars agree that the excess density around these galaxies must be, taking a liberal estimate of the possible background density of quasars, between 10 and 30 times that background density. This is the same result that was the conclusion of the first, much maligned paper. Apparently the chance of accidentally getting an overdensity by the original factor of 20 is about 10"" (or more accurately, 7 x 10"16 )•
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The final published data and exhaustive analysis, however, made no difference. It was sufficient for many astronomers to have something—anything—in print claiming the associations were spurious. This was brought home with particular vividness after a physics-astronomy conference in Geneva in
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November 1983.1 was chatting with a British cosmologist about C fields and inflationary theory when the subject of quasars was mentioned. This theorist looked distressed and said apologetically: "Well, I was interested in your quasar investigations, but then I was told your observational evidence had been proved wrong."
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It was clear that the research had been successfully discredited.
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But, before that I was even more painfully aware that the event had been used with disastrous effect within my own home observatory. While the critical paper that had been published so quickly in the Monthly Notices was still in preprint form, it had also been sent, special communication to the new director of my observatory, courtesy of the most eminent quasar researcher on the Caltech faculty. This occurred shortly after Caltech had broken the agreement to jointly operate Palomar Observatory with Carnegie Institution of Washington.
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Soon after this, a friend of mine met the director at the airport in Washington, D.C., and asked about me. The answer came back:
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"Well, I wish he would get his statistics right!"
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When I heard this, I went to his office
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The Battle Over Statistics 25
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at<o:
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17mag.
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APPARENT MAGNITUDE OF QUASAR ( V 5 0 0 0 )
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Figure 2'5. The excess density of quasars around companion galaxies. Bright, medium, and faint quasars are aR between 10 and 30 times denser than in (he average field.
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and put down on his desk a copy of my final paper in which I had recalculated all the statistics using a different method and verified the original answer. Weeks later, in a talk with him, however, he spoke angrily about ludicrous arguments on my part and finally said, in effect:
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"No matter what you do, you will never be able to prove that you are right. If you are right it will have to proved by someone else."
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Afterwards, I reflected that this was truly a serious crisis when a scientist admitted that he could not be convinced by any possible scientific evidence, and moreover, that personal prejudices played a part in judging the experimental evidence.
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Of course an infallible method exists for even highly placed scientists to get into big trouble—that is simply to get the "wrong" answer. This was vividly demonstrated, aside from the papers referenced earlier in this chapter which supported the associations, by the case of the then director of the Kitt Peak National Observatory, G. R. Burbidge. Together with some collaborators, he had sub-
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mitted a statistical analysis on this subject. The study utilized the extremely valuable, complete catalog of all known quasars that had by then been compiled in collaboration with Del Hewitt. The sophisticated statistical analysis showed again strong evidence for correlation of quasars with bright galaxies. The referee's report on this paper excited wonderment in all those who gazed at it. As is all too common these days, the anonymous referee utilized trivial criticisms and inapplicable arguments against the paper. Since there was no sign of this obvious blocking coming to an end, or any intervention by the editor, it was sent to another journal. That journal sent it to another astronomer, who prides himself on his scientific intransigence, and it was rejected out of hand. Would the paper ever appear or would it become a rare, suppressed collector's item? Happily, it was finally published in 1984 in Astronomy and Astrophysics, another strong confirmation of the association of quasars with relatively nearby galaxies.
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Perhaps an equally vivid demonstration of how the publication of scientific results can
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26 The Battle Over Statistics
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AKS
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i/)
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^ 20
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IX.
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IT 10-
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PROBABILITY OF FINDING QUASAR
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Figure 2-6. The im/robabilit} of quasar associations with companion galaxies plotted against the number observed. Expected relations for observed random background (I) and ten rimes density o/observed background (11). From DuBois, Giraud, and Vjgier (1983).
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be hampered is the case of a paper by the creative and knowledgeable French physicist, Jean-Pierre Vigier, and two collaborators. Seeing the attack on the statistics of the association of quasars near companion galaxies, they carried out an analysis of their own. Figure 2-6 above shows that they made yet another, but very elegant approach to the problem. They plotted the number of quasars found near companions as a function of the improbability of finding them. Then, as Figure 2-6 shows, they calculated the expected probability of such proximity if the quasars were distributed randomly with respect to the galaxies. The figure shows that even if the background density were an order of magnitude (ten times) greater than the value it is actually measured to be, the quasars still, very obviously, fell much closer to the galaxies than could be explained by chance. The fate of this paper did not involve much suspense. It was rejected without hesitation by the same journal that published the original, supposed refutation. This confirmatory paper wound up being published in the Comptes Rendus de I'Academie des Sciences Paris. A noble publication in the past, Comptes Rendus, with papers like this, might have to become more regular reading for those few astronomers who wish to know "how it really is."
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Perhaps none of these occurrences would be any more serious than confrontations between opinions in science and human affairs of the kind that have taken place many times in the past. What has happened in astronomy today, however, is that almost all telescope access has been shut off to the proponents of one point of view—namely the point of view that current assumptions should be subject to observational test and that contradictory and surprising evidence should be followed up. The irony is that previously no more than about 5 percent of telescope time was given to projects that explored outside of the conventional, run-of-the-mill beliefs. To add this 5 percent additional time to the routine programs makes no significant contribution to them; it merely has the effect of suppressing all the discovery-mode programs. In a way, it is testimony to the extreme fear that the opposing side has of this kind of research that they would ruthlessly seek out and subdue this small effort. On the other hand, it raises the question of whether the enormous financial, engineering, and administrative effort put into astronomical research today is being wasted at the point of application by scientists who believe they already know all the important answers.
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The Battle Over Statistics 27
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Appendix to Chapter 2
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There are many references to the events described in this chapter. Some of the main papers are referenced below and the remaining references can be gleaned from a reading of these papers:
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1970, Arp, H., Astron. Journ., 75, p. 1. This is the first paper testing the association of real quasars with bright galaxies versus randomly generated sets of
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quasars. The line of quasars near NGC 520 and differences in quasars between the direction of the center of the Local Group of galaxies and the supergalactic center are first introduced. The latter subjects will be amplified in later chapters of this book.
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1971, Burbidge, G. R., Burbidge, E. M., Solomon, P. M., and Strittmatter, P. A., Astrophys. Journ., 170, p. 233. This is an investigation of an independent set of quasars falling close to bright galaxies. The analysis shows
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accidental chances are less than five in a thousand.
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1972, Burbidge, G. R., O'Dell, S. L., and Strittmatter, P. A., Astrophys. Journ., 175, p. 601. This analysis showed quasars associated with more distant galaxies fell closer to the galaxies on the sky as if viewed
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from a greater distance. This relation was confirmed and expanded by Arp in 1983 (see below). The discussion in the Burbidge, O'Dell, and Strittmatter paper developed all the properties of the quasars' distribution in space which had to pertain if they were more local than their redshift distances. These distribution properties were later confirmed by subsequent evidence discussed in this book.
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1973, Arp, H., Confrontation of Cosmologkal Theories with Observational Data, IAU Symposium No. 63, ed. by M. S. Longair, D. Reidel, Dordrecht, Holland, p. 61.
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This is a brief summary of observational evidence for nonvelocity-caused redshifts to that date. It gives the first evidence for absolute luminosities of quasars as a function of their (intrinsic) redshift which will be elaborated in later chapters.
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1973, Arp, H., Evidence for Nonvelocity Redshifts—New Evidence and Review, IAU Symposium No. 58, ed. J. R. Shakeshaft, D. Reidel Publishing Co., Dordrecht, Holland, p. 197.
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This is a review of work up to 1973 and points again to the quasars near redshift 2 being the less luminous quasars and projected at relatively large separations from very nearby galaxies. This prevision is confirmed and elaborated in the more recent results in Chapter 5 of the present book. Just before this presentation at the IAU in Australia (page 195), W. L. W. Sargent gave a statement of the conventional beliefs in this field. It is interesting to read these two papers to contrast the nature of the evidence used. In those days, many astronomers were actively interested in the discordant evidence and it is extremely interesting to read the recorded debate that took place after each of these papers.
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1980, Weedman, D. W., Astrophys. Journ., 237, p. 326. This is the analysis that purports to demonstrate no association between quasars and galaxies but uses an
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inhomogeneous sample of too distant galaxies.
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1981, Sulentic, J. W., Astrophys. Journ. (Letters), 244, p. L53. This paper repeats the analysis and shows that the quasars are indeed associated with bright galaxies as they were
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originally reported to be in the papers commencing in 1966
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1982, Webster, A., Mon. Not. Roy. Astron. Soc, 200, p. 47. The first strong attack against the statistics of the association of quasars with companion galaxies. This is the paper
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that, though incorrect, was generally accepted as the refutation of the association.
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1982, Browne, I. A. W., Astrophys. Journ. (Letters), 263, p. L7. This and the reply immediately following it in the Journal discusses some of the pros and cons of calculating
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statistics in various ways.
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1983, Arp, H., Astrophys. Journ. (Letters), 271, p. L41. This is the addendum which, with great difficulty, I succeeded in getting published. It discusses the Note Added in
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Proof to the Browne (1982) paper and points out errors in the Webster (1982) analysis.
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1983, Zuiderwijk, E. J. and de Ruiter, H. R., Monthly Notices of the Royal Astronomical Society, 204, p. 675. This is an independent calculation on the Arp data dealing with quasars near companion galaxies. The authors find
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evidence that the two kinds of objects are associated. The significance of their association would be much stronger, however, if they took into account the different distances of the galaxies in the sample. For example, the quasar somewhat brighter than 16th mag. about 1/2 degree from NGC 3077 (a companion to M81), is just as much a
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28 The Battle Over Statistics
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confirmation of the association as fainter quasars, found at smaller separations from galaxies much more distant. 1983, DuBois, M. A., Giraud, E., and Vigier, J. P., Comptes Rendus Acad. Sci. Paris, 26 Sept. 1983, Serie II-259.
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This paper gives a different and elegant statistical confirmation of the associations between quasars and galaxies. 1983, Arp, H., Astrophys. Journ., 271, p. 479.
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This is the final paper completing the observations and recalculating probabilities by a different method, and which confirms the original Arp calculation. 1984, Chu, Y., Zhu, X., Burbidge, G., and Hewitt, A., Astronomy and Astrophysics, 138, p. 408.
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This is the most recent paper confirming the association of quasars with nearby galaxies.
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The Battle Over Statistics 29
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GALAXIES VISIBLY 3 CONNECTED TO QUASARS
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I t seems exceedingly strange to have battled so hard about statistics when direct photographic evidence of physical connections between quasars and low-redshift galaxies has existed all along. We saw one example of this in Figure 1-3. But here I will recount briefly the saga of a much more famous case, the greatly tortured history of the galaxy NGC 4319 and its nearby companion. The story begins with the astronomer called Markarian who surveyed the sky for objects with strong ultraviolet continuum radiation using a small Schmidt telescope in Armenia. He found among his hotly radiating objects the quasar-like object, called Markarian 205, close to the edge of a spiral galaxy. Daniel Weedman obtained spectra and announced that it had a redshift of z = 21,000 km s'1. But the galaxy only had a redshift of z = 1,700 km s-1.
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Naturally, I was interested whether any effects were visible in the two objects which might give direct evidence that they were close to each other in space. To make sure, I took the deepest photograph possible, using the high-detectivity Illa-J film that Eastman Kodak had manufactured especially for as-
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tronomy. It required a four-hour, sky-limited exposure at the prime focus of the 200-inch reflector at Mt. Palomar. When I developed the photograph I was surprised and excited to find a luminous connection between the quasar and the galaxy. Naturally, the first thing I did was to ask myself whether this could be some kind of artifact, or was it a real luminous connection. An observer experienced with large telescopes (the older variety of observers at least) can look at a photographic plate and ascertain from the sharpness, shape, and extent of an image whether it is likely to be an emulsion defect or a real object in the sky. This object was clearly real. The next question which naturally presented itself was: Since the quasar and galaxy were close on the plate, could this apparent connection be due to overlapping of projected images, that is, a bleeding together of the light distribution around accidentally projected background and foreground objects? A few moments' thought indicated that unrelated images melding together would produce an hourglass-shaped image. But, in fact, the photographed connection was relatively narrow and straight-sided ruling out anything
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Quasars Visibly Connected 31
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NGC43I9 MARK 205
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other than a real physical connection. Figure 3-1 shows this now-famous photograph.
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Well didn't it rain! A number of photographs that did not show the connection were soon circulated. It got so bad that at the 1973 meeting in Australia I projected a short exposure of the system, explaining that I did not want people to think I was a bad photographer, and that I too could obtain an exposure that did not show the connection. The feeling that was communicated from little groups of astronomers who would stop talking as I approached was that for the sake of the honor of science they would graciously assume that my original report had been misled by some transient artifact.
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The published paper that had the most effect in this little drama was a rather pretentious effort by two researchers at another observatory. With a telescope smaller than the one I had used to obtain my picture, they ob-
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Figure 3-1. The quasar-like Markarian 205 is just below the disrupted spiral galaxy, NGC 4319. Note the straight, luminous connection between the two. This is the original discovery photograph (Arp 1971).
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tained a new picture. (The ratio of their 2meter to the 5-meter I had used gives 2/5 squared = 0.16 of the photons.) They proceeded to give the definitive analysis of the system in the following terms: (1) The connection was not there; (2) Just in case it was there, it was accounted for by a background galaxy lying accidentally in just the right position to appear like a connection. In actual fact, the connection had much too low a surface brightness to be a galaxy seen edge-on. The connection was also straight-sided, whereas an edge-on galaxy would have to taper at its ends. But the taper of an edge-on galaxy would have to be opposite the hourglass-shaped cusp of two images optically melding together, which was the third favorite explanation advanced for the feature. In fact, looking back now, their picture showed quite well the straight-sided connection that was to be confirmed so clearly with later techniques.
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32 Quasars Visibly Connected
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But an amalgam of these contradictory rationalizations was soon accepted as sufficient justification for retaining the conventional view that objects with such different redshifts could not be physically close together.
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In all this technical obsfucation, however, a very common-sense point was overlooked. The galaxy, NGC 4319, is an extremely unusual galaxy. It is literally coming apart, as Figure 3-1 or any of the many pictures in the literature attest. There might be a weak attempt to claim there is another large galaxy some distance away that is interacting with NGC 4319. But there are no sheared plumes or asymmetric gravitational tides present in NGC 4319. It is simply that the arms are coming off at the roots in NGC 4319! It is as if this was a normal, two-armed spiral galaxy that had recently (of the order of ten million years ago—a fraction of a galaxy rotation period) suffered some explosion or internal perturbation that simply caused the spiral arms to disintegrate at their base where they normally join the main body of the galaxy. As a long-time observer of peculiar galaxies, I can assure you that this is an extremely unusual spiral galaxy.
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The importance of the luminous connection reaching from the quasar-like object back to the galaxy is that the connection goes straight back towards the galaxy's nucleus. This provides rather direct evidence that the quasar emerged from the nucleus. Since nuclei of many galaxies are active, in the sense that they emit high-energy radiation, show variability, and eject radio sources and luminous material, it is logical to conclude that this quasar has been ejected from the nucleus of NGC 4319. If the conditions in the nucleus of the galaxy from which it has been ejected are abnormal, the material out of which the quasar itself is constructed may very well be intrinsically abnormal. We will develop this theme in coming chapters but it has always seemed to me that their probable
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ejection is the biggest single clue to the nature of quasars. Of course, this makes the whole question of the reality of the connection absolutely crucial.
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The question appears to have been resolved by an analysis performed eleven years later by Jack Sulentic with the powerful image-processing facilities of the Jet Propulsion Laboratory in Pasadena. The large computers that had been used to process the pictures of planets and moons sent by the world's first space voyagers had also been programmed with sophisticated algorithms which could extract the maximum information contained in any medical pictures, highaltitude pictures of the Earth's surface and even astronomical photographs. Jean Lorre— who has unfortunately left the imageprocessing laboratory now— tutored Sulentic in what are still today the most advanced techniques of image processing. Sulentic selected from photographs which had been collected during the 11-year interval the four best plates taken with the 5-meter telescope at Palomar and the three best plates taken with the 4-meter telescope at Kitt Peak National Observatory (KPNO). From this new and independent plate material obtained with the best telescope he produced the picture shown in Figure 3-2.
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Figure 3-2 looks just like the original Arp photograph in Figure 3-1. It seems as though the connection does exist! Furthermore, by using the technique of mathematically filtering the information contained in the photographs, Sulentic was able to show a very narrow, sinuous connection inside the broad connection which can be traced well back through the inner regions toward the nucleus of NGC 4319.
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The implication of this is crucial. It implies that the quasar-like object, at least as it traversed the galaxy disk, was very small. This makes good sense, and in fact would almost have to be true, if the object was to emerge from within the small dimensions of the cen-
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Quasars Visibly Connected 33
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Figure 3-2. This is the confirmation of the connection between N G C 4319 and Mark 205 from the summation of 7 additional plates
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- - i " ' v - / . G : - • • : • by lack Sulentic (1983).
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tral nucleus, where the activity of galaxies two objects quite plainly—in fact, if you held
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seems to be centered. At this later date, the the magazine at arm's length the connection
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luminosity of the quasar may be higher than virtually leaped off the page!
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when it emerged. In any case, it now burns
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In view of the massive negative folklore
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out a large region around its center. It would that had preceded Sulentic's image-processed
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be extremely interesting to see just how small picture of the luminous bridge, we thought
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a center the light in Markarian 205 presently that perhaps a little overkill might not hurt.
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defines. A few seconds of exposure with the Also, we were interested in finding out more
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Hubble Space telescope would give us this in- about this object, so we applied for time on
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formation.
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the 4-meter KPNO telescope, which had
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But, the feuding over Markarian 205/ been equipped with the newest highly quan-
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NGC 4319 was far from over. The observers tum efficient CCD's (charged coupled de-
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A. Stockton, P. Wehinger, and S. Wyckoff, vices) for direct imaging. It took the personal
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had been taking and analyzing photographs of intervention of the director, G. R. Burbidge,
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the system and claiming that the connection to get us a couple of nights on this instru-
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was not real. The latter two authors went so ment. But with these few hours we were able
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far as to publish pictures in pseudo-color in to obtain images of the object in several dif-
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Sky and Telescope. In a brief article they man- ferent colors. By that time, I had taken tem-
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aged to mention three times in three para- porary refuge at ESO (European Southern
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graphs that the quasar must be a background Observatory) in Munich. Since they had good
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object. They ended with the statement that computer reduction facilities, I personally did
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their Hawaiian observations had established the image processing on these new CCD
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this "beyond a doubt." Their article caused frames. I used pseudo-color to delineate the
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some amusement because their pseudo-color bridge in living scarlet as shown on the jacket
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pictures showed the connection between the of this book and in black and white in Figure
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34 Quasars Visibly Connected
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Figure 3-3. The picture shows the addition of CCD frames taken at the KPNO 4-meter telescope. The isophotes which best show the bridge between the two objects are colored red in the picture which is on the jacket of this book (Arp and Sulentic, unpublished). The insert shown here in the central region of the galaxy uses image processing to reveal a narrow cenmil spine.
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3-3. We joked that perhaps we should make up T-shirts with a superposed outline of the Golden Gate Bridge between the two objects. We abandoned the project, however, when we considered how little sense of humor there was in the field. At any rate, Figure 3-3 is not bad for the bridge that could not be!
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The atmospheric steadiness was not good enough on these particular nights to confirm the very thin sinuous connection back to the nucleus. But, the linear intensity response of the sensitive detector allowed image processing of somewhat broader features in the interior by Sulentic which revealed a narrow central spine stretching outward in either direction from the nucleus of the spiral galaxy. This central spine is shown in the inset in Figure 3-3. This latter feature is important for three reasons: First, it demonstrates once again that this is a highly unusual galaxy; sec-
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ond, that this unusual feature is associated with the luminous bridge to Markarian 205; and third, that this relatively thin feature suggests a counter-ejection in the opposite direction from the hypothesized ejection of Markarian 205. In astronomy, jets tend to have counter-jets, radio-source ejections tend to occur in opposite directions and, in general, to conserve a momentum in any ejection process one would expect a counter-ejection. It was therefore with considerable excitement that Sulentic spotted a stellar-appearing object in our ultraviolet CCD frames. It was almost exactly at the end of the spine, opposite to Markarian 205. After scrambling to get time on the 4-meter again (the Palomar 5-meter had by this time been completely closed off to us), we tried to get spectra of this faint blue object buried in the disk of the galaxy. We are not sure we got it. There was a little emission on
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Quasars Visibly Connected 35
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some of our spectra near this position. Perhaps this is an H II region as found normally in spiral galaxies. Perhaps this kind of a hydrogen emission (H II) region, as in some other objects, is an indicator of recent ejection activity. Perhaps this is some gas heated by a continuum source of unknown nature. We need more investigation of this region.
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But all of the spectra throughout the disk of NGC 4319 that we did get revealed an unexpected aspect. The hydrogen-alpha emission that normally characterizes spiral galaxies was almost completely absent. Pervading the entire disk was, instead, only emission from ionized nitrogen. This is very unusual for a spiral galaxy and, again, hints that violent events may have recently taken place. This observation also needs to be followed up.
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An interesting footnote to the controversy over Markarian 205 and NGC 4319 is that a Caltech astronomer and a regularly collaborating fellow British scientist were in the favored position of regularly obtaining the biggest blocks, really enormous amounts of time, on the 5-meter telescope at Mt. Palomar. One of their favorite observing programs attempts to examine high-redshift objects close to low-redshift objects. If they detect absorption lines of the low-redshift objects in the spectra of the high-redshift objects, they announce them as proof that the highredshift objects are the more distant. Of course, the high-redshift object could be just behind the low, or even imbedded in it, or, if it was ejected, have pulled out a plume of the low-redshift material around it. Be that as it may, when they don't find the low-redshift absorption, there is an implication that the high-redshift object is in front. (This is not ironclad, of course, because we may be looking through a "chink" in the low-redshift object.) But in the case of NGC 4319 just discussed, the material in the galaxy is so spread around, that it would be difficult to imagine finding a column to look through that was free from low-redshift gas. So I noted
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quietly the information that had been leaked to me about a year before that they had looked hard for low-redshift absorption in the spectrum of Markarian 205. From the floor of the Liege meeting in 1983,1 asked what they had found. They replied that they had found no absorption. What seemed to me quite devastating was that they had to publicly admit that they had not published information gained from those enormous amounts of large telescope time, that they had withheld this important scientific information apparently because it did not agree with the position to which they were committed.
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The most recent development in the saga of this system is quite spectacular. Thanks to the dedicated perserverance of Sulentic, he was able to obtain 6 hours of observing with the Very Large Array radio telescope. His results are shown in Figure 3-4. This, the most sensitive radio map obtained to date, now clearly shows extended lobes of radio emission on either side of the galaxy. Therefore, like other examples of ejecting galaxies, NGC 4319 also turns out to have ejected radio material on either side of its nucleus. It is an enormously rare spiral galaxy, however, which shows such ejected radio material beyond its nucleus. (One other, NGC 4258, will be discussed in Chapter 9.) The rare, quasarlike object, Markarian 205, is further in toward the nucleus than these extended lobes and its line to the nucleus is rotated slightly forward, in the direction of rotation of the galaxy, as if it were a slightly later ejection. The explosive disruption of the galaxy is also confirmed by the observation of the ejected radio lobes. The grand, final question now becomes: "Does all this evidence finally add up to conclusive proof of what was immediately evident from studying the first photograph: namely, that these two cosmic objects of extremely different redshifts are physically related, that in fact the higher redshift, compact object has been ejected from the lower redshift galaxy?"
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36 Quasars Visibly Connected
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N4319
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IPOL 1464.908 (1H2 NAT-AB.ICLN.l
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75 38
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37 38
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36 30
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35 30
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34 30
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12 20 00
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B. The Quasar PKS 1327-206: Another Quasar Connected to a Peculiar Galaxy
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If the preceding examples which have been discussed were not sufficient, the most conclusive example of a quasar connected to a galaxy turned up during the writing of this book. The way in which it surfaced is perhaps as revealing as the fact of the association. As just mentioned, one of the most popular types of time allotments on telescopes involves long exposures on the spectra of quasars near galaxies. The game is to search for absorption lines in the quasar due to the "foreground" galaxy and thus to study the halo surrounding the foreground galaxy. (This postulated halo is not optically visible.) As usual, no result is too "gee whiz" not to be easily fitted into a model of halos. (Of course, it is strongly preferred that examples of quasars close to galaxies are discovered by observers of cosmological rather than local persuasion.)
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Figure 3-4. Radio emission from N G C 4319 as measured by Siientic with the Very Large Array radio telescope (at 20km wavelength). The radio isophotes are superimposed on a photograph taken in red light with a CCD detector. Radio lobes are seen on either side of the nucleus of the galaxy, and the quasar, life examples which follow in this chapter, is very near one of the radio lobes.
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In this particular case, I was in Paris giving a series of lectures on the latest evidence for association of quasars with nearby galaxies. Announcements of these lectures had been widely posted, but during the course of these weeks, I took the occasion to call on some close astronomical friends who did not know I was there. Naturally, they began to entertain me with their latest results on galaxy halos by using quasars as test probes in the background. I was listening politely to tales of a particular unusual halo when I casually asked, "What does the adjacent galaxy look like?"
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There was a considerable silence after which it developed that they, neither separately nor together, had ever looked at pictures of the pair of objects they were studying—at least not at the best pictures, which were available to everyone in the form of the Schmidt telescope Illa-J sky survey. I immediately proceeded to consult the nearest cataloged photographs. It turned out that two
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Quasars Visibly Connected 37
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Figure 3-5. The quasar, Parities 1327-206 connected by a luminous filament to a galaxy with a jet. Print is from two survey plates taken with U.K. Schmidt telescope in Australia. Copyright Royal Observatory, Edinburgh.
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independent photographs of this system existed and both plainly showed a luminous filament connecting the quasar to the galaxy. Figure 3-5 shows the combined print of these two survey photographs.
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The analysis of this photograph seems very simple to me. There are only two possibilities. Either the quasar placed at the head of the filament is an accident, or the two objects are physically connected. Since the configuration has negligible probability of arising by chance, I conclude that this demonstrates the physical association of quasar and galaxy. There goes the whole cosmological quasar hypothesis!
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I might remark that one interpretation of what is going on in this picture might be that the quasar originated at a point that is now in the strong jet which emerges from the galaxy, and that both quasar and galaxy have moved
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away slightly from that point since that time of origin. Another interpretation, since the quasar is quite bright in apparent magnitude, is that, along the lines of Chapter 5, they could both be close to us in space and have been expelled by a nearby galaxy. They might also simply represent a rare accidental collision of a galaxy and quasar in the same locality of space. One thing that is inescapable, however, is that the high redshift quasar is at the same distance as the low redshift galaxy.
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Another aspect that is inescapable, unfortunately, is that there was a considerable amount of throat-clearing and sidelong glances but that picture was not rushed into the scientific literature. In fact, it was not published at all. I am conducting a two-part scientific experiment with this object. The proposition is that when conclusive evidence for the association of high and low redshift
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38 Quasars Visibly Connected
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objects exists, it goes unnoticed. When it is pointed out, it is not published. The first part of the proposition has already been verified. The second part of the proposition is being tested. 1 made photographs of the objects available in June 1984. My prediction is that the pictures will only become available with the publication of the present book.
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There has been another interesting mechanism at work over the years which I am only now beginning to appreciate to its fullest. It goes something this this:
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"This is a very impressive picture of a high-redshift object connected to a lowredshift object. If you can show me another one of these, I will have to take the matter seriously."
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When the next, but even more striking object is discovered:
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"Oh now, this is really impressive. Forget the first one. It requires another one of these."
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C. NGC 5297/96 and Other Galaxies Optically Connected to, or Perturbed by, Quasars
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Featured on the cover of the published proceedings of the Paris Conference of 1976 was a large spiral galaxy, NGC 5297, with a conspicuous companion galaxy, NGC 5296. It is shown here in Figure 3-6. A diffuse, luminous connection extends from the companion in toward the main galaxy and a similar extension in the other direction terminates on a quasar.
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The story of this quasar's discovery may seem unbelievable to skeptics, but I do have a witness. Jack Sulentic and I were going through the Palomar Sky Survey prints making identification prints for our next telescope run. I spotted this galaxy with its companion and said, "That's the kind of companion that should have a quasar." We looked at the nearest star to the companion and it was blue. We
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took a spectrum that run and it turned out to be a quasar. (This occurred before the systematic search for quasars around companions which was subsequently performed in another area of the sky, as described in Chapter 2.) The chance of accidentally finding a quasar both this bright and this close to NGC 5296 is only about 0.002 or 2 chances in a thousand. After the quasar was confirmed, the deep photograph shown in Figure 3-6 was obtained with the 200-inch telescope. It was then discovered that there was a low surface brightness filament leading from NGC 5296, narrowing as it approaches the quasar and ending almost exactly on the quasar.
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On this same deep plate a small compact galaxy was seen silhouetted against the companion galaxy, NGC 5296, which meant that it had to be spatially in front of the companion. Yet, the compact galaxy's redshift is more than Az = 23,000 km s~' greater. This is the first example we have encountered of a galaxy, an object with larger apparent diameter than the generally point source quasars, which has an "excess" or nonvelocity redshift. In Chapter 6 we will see many examples of galaxies with excess redshifts and propose a way in which the anomalous redshifts of these galaxies are related to those of quasars.
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At the Paris Conference, further cases were reported of a companion galaxy with a luminous filament pointing toward a nearby quasar (NGC 5682, shown here in Fig. 2-3, also accompanied by a nearby, high-redshift Markarian Object). Reported in addition was a quasar within the envelope of a peculiar E-galaxy, apparently perturbing it (NGC 7413). Another high-redshift, very peculiar object was found silhouetted in front of the outskirts of the nearby E-galaxy (NGC 1199).
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In the decade since these discoveries were announced there has been no serious followup observations by other astronomers. In fact, there has been a clear effort to avoid these objects.
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Quasars Visibly Connected 39
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Figure 3-6. The spiral galaxy N G C 5297, and its companion galaxy NGC 5296. Arrows indicate quasar ofredshift z = 0.96 and silhouetted high-redshift galaxy ofredshift z = 25,900 km s"1.
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D. Radio Connections—The Radio Galaxy 3C 303 and Nearby Quasar(s)
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Not all radiating filaments emerging from galaxies are seen in visible-light wavelengths. In fact, it is much more common to see jets of radio-emitting material emerging from galaxies. It is believed that inside these radio jets are ionized gases (plasmas) where the motions of the charged particles are bent by magnetic lines of force causing radiation. (Accelerating or decelerating electrons produce so-called synchrotron radiation which, for the lower energies, is generally detected as radio emission.) What causes these jets is more or less a mystery, although most theorists talk about a "beam" of energetic particles being ejected somehow from active galactic nuclei. Now, I personally have severe doubts whether beams can explain the observed morphologies—the jets are in many cases too thin and parallelsided and the "hot spots" (compact regions of intense radio emission) observed in the outer
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lobes tend to trail behind the jets. But if compact bodies can be ejected from nuclei, as the evidence just described implies, perhaps a more or less continuous stream of particles can accompany them. Alternatively if a beam of smaller particles becomes narrow enough and in addition must turn off and on, i.e., be pulsed, perhaps it approaches, in some sense, our crude concept of whatever a compact quasar-like or proto-quasar-like object might be during its ejection from a galaxy. Perhaps it does not pay to be too dogmatic at this stage about just exactly what is ejected from these nuclei.
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Regardless of the exact composition of the jet, however, if we observe a quasar out near the end of a radio jet where it has low probability of appearing by accident, it becomes an additional demonstration of the association of quasars with lower redshift galaxies. The quasars then are connected to the galaxies not by an optically radiating fila-
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40 Quasars Visibly Connected
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3C303 4866 MHz 52° 14'28"
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24"
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o 20"
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Q
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optical position of galaxy nucleus
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16"
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QUASAR
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h ms
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14 41 25.0
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24.0 RIGHT ASCENSION
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23.0
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Figure 1-7. The radio galaxy 3 C 303, showing ejected radio material to the west which ends near the objects discussed in the text. Radio map from P. Kronberg, E. M. Burbidge, H. E. Smith, and R. G. Strom.
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ment as before, but by a radio radiating filament. Several examples of this exist and one of the best known is shown in Figure 3-7. In that figure, we see the radio filament extending westward to where it terminates at the position of three, stellar-appearing, ultraviolet objects. One of these objects has been confirmed to be a quasar by E.M. Burbidge, P. Kronberg, H. E. Smith and R. Strom. The other two are somewhat too faint to get a decisive spectrum on. But the expectation would have to be that they also are some kind of quasars or quasar-like objects. The probability of getting three such objects so close together is extremely small, marking this configuration as a very unusual one. But, just considering the one confirmed quasar, we see that it falls only 5 arcsec from the tip of the radio jet. By the precepts of Chapter 1 the chance of this occurring by chance is something like < 10"4. This example therefore pro-
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vides additional, very strong evidence for the connection of a relatively low-redshift galaxy with a quasar.
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E. The Radio Galaxy 0844 + 31
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|
Curiously enough another radio galaxy looks quite similar to the one we have just discussed. This latter galaxy is called 0844+31 (after its position in the sky), or 4C 31.32 (after its position in the 4th Cambridge Catalog of radio sources). The radio map of this object is shown in Figure 3-8.
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A strong radio jet proceeds roughly northward from the galaxy. It ends in a lobe of radio emission within which there is a "hot spot." This hot spot curves around in a southerly direction and ends about 5 arcsec from a quasar. Again, by using the average quasar density discussed in Chapter 1, we can calculate the chance of a quasar this bright acci-
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Quasars Visibly Connected
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41
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0844+31
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DEC.
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R.A.
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dentally falling this close to the tip of the hot spot: it is 3 x 10^. That is less than one chance in 330,000. Even if we say the significant distance is from the quasar to the center of the radio lobe, about 19 arcsec, the chances of accidental occurrence are only 4 x 10'5, or about one chance in 25,000.
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But how many chances did we have to accidentally discover these quasar juxtapositions with radio jets? In the most recent compilation, A. Bridle and R. Perley list only 75 galaxies with redshift z :£ 0.2 that have radio
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Figure 1-8. The radio isophotes of
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the galaxy 0844+31 measured at
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6-cm wavelength. The cross shows
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the position of a quasar with z =
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\ 1.83. Observations by W. van
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2'
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Breugel.
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jets. For the astronomers who studied these objects, just unavoidable encounters with known quasars have turned up the two associations in this list (0844+31 and 3C 303) both at an improbability level of less than 10~4. What would a quasar search around the rest of these radio jets reveal? My casual inspection of the list indicates there may be as many as eleven associations, at about the 0.01 level of improbability, of radio-jet galaxies with already known active objects of higher redshift in the vicinity, some- with good alignment
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42 Quasars Visibly Connected
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with the radio jets. These associations "get no respect" be-
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cause in each individual case the highredshift object is dismissed as an unrelated background object. Then, each case is forgotten. One of the purposes of this book is to collect together these neglected cases in order to show that they are not isolated incidents but together furnish another powerful confirmation of the ejection origin of quasars and quasar-like objects from active, low-redshift galaxies.
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Actually, when unusual objects like quasars fall this close to the end of a radio or optical jet, the question should not be: Can we measure a slight separation between the two which we can use as an excuse to ignore the observation? After all, as discussed in this book, a lot of independent evidence strongly established these kinds of associations. The question should be, what does the slight separation mean? Are quasars and compact objects slightly preceding, or trailing, the connection? Are they exhibiting the same kind of behavior as the ejected emission regions in the galaxy, NGC 1808, where G. Schnurr reports a line of blue luminous regions slightly separated from the hydrogenalpha emitting regions? Is the optical object a leading precursor or a later development in the ejection? Can compact objects power the radio lobes, and are they the source of in situ energy injection?
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F. A Quasar and Compact Radio Sources Ejected from The Radio Galaxy B2 0924 + 30
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During the course of a survey of radio sources with the radio telescope in Bologna, Italy, a very interesting radio galaxy was discovered. Like so many radio galaxies, this one had lobes of radio emission stretching away on either side of it. The lobes are material ejected from the nucleus of the galaxy, ac-
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cording to the accepted belief. But, in this particular case, three very compact radio sources are almost perfectly aligned with this ejection. The authors of this paper, R. Ekers, R. Fanti, C. Lari, and M.-H. Ulrich, calculated the chance of these compact sources being so situated was only about 10~5, or one in a hundred thousand. Yet the nearest compact source was almost touching one of the large outer lobes of the radio galaxy!
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Figure 3-9 shows this configuration. Since I was observing on the 200-inch telescope in those days, I was able to measure the extremely faint optical object at the position of the nearest compact radio source. It was a quasar of redshift z = 2.02!
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There are several comments we can make about this:
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With the powerful radio telescopes now available (at considerable public expense) this region could be mapped to much fainter contour levels. It is quite possible the slight space between the quasar and the extended radio lobe would then turn out to be filled in by radio emission, furnishing a continuous connection between the ejected material of the galaxy and the quasar. In any event, a deeper radio map could give critical information on the kind of connectivity or interaction that this quasar had with the lobe, if indeed it does interact.
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The second comment is that this system could be critical for understanding the way in which galaxies eject quasars. Since the quasar which was observed was so optically faint, the system could be fairly distant and there could well also be quasars even fainter, which we cannot yet see, at the positions of the two other compact sources. If the outer two compact sources are quasars, why are they fainter? Are they closer to their birth? If so, measuring their redshifts would be critical because it might confirm the suggestion that quasars are born with very high redshifts and evolve toward brighter, lower-redshift objects with time. In other words, quasars might represent
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Quasars Visibly Connected 43
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Figure 3-9. The radio galaxy B2 0924+30, showing ejected radio lofces and aligned compact radio sources. The nearest compact source to the southwest radio lobe is a quasar ofz = 2.02. Radio contours jrom Ekers, Fanti, Lori, and Ulrich.
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the birth of galaxies as in conventional theories, but they simply start small and grow larger. Furthermore, there may be many such emerging sources located throughout much of relatively nearby space.
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Of course, there are many other possibilities. One is that the outer compact sources were ejected at greater speed or that they were ejected at an earlier time. The outer sources might also be different kinds of objects, or the speed of ejection may have had some effect on the rate of their development, so that they are now still below our limit of detection. Large telescopes exploring the region of the outer compact radio sources like these could reveal important new information which would aid in understanding just how fast quasars are ejected and how rapidly they evolve. But who will use large telescopes for those investigations?
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We can summarize the content of this chapter by saying there are a number of exam-
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ples already known of an "experimentum crucis" where a quasar is seen linked directly to a low-redshift galaxy. Any one of these is sufficient to establish conclusively that quasars can be much closer than their redshift distances. But a number of these conclusive cases now exist. And, of course, this is all in addition to the statistics of multiple and single associations developed in the first two chapters, which I also feel are conclusive.
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The very close separation of one to three quasars from a galaxy or the visible connection to a specific galaxy, however, are far from the most common form of associations. In the coming chapters we will see that the most common form of quasar associations is in groups and lines at many diameters from their galaxies of origin. These associations are generally supported by the morphology of the central galaxy, the distribution of radio material and the distribution of X-ray material in the vicinity.
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44 Quasars Visibly Connected
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TABLE 3-1 Quasars Connected to Galaxies or Close to Radio Lobes
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GALAXY
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QUASAR
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Name NGC4319
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Redshift km/s 1,700
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Name Mark 205
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Dist. (arcsec) 40
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Mag. 14.5
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|
Redshift (z) 0.07
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|
Chance Probability
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|
~0
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|
MCG 03-34-085 5,400
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|
|
NGC 5296
|
|
|
|
2,500
|
|
|
|
3C303
|
|
|
|
42,000
|
|
|
|
PKS 1327-206 38
|
|
|
|
BSO#1
|
|
|
|
55
|
|
|
|
UV#C
|
|
|
|
20*
|
|
|
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|
|
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|
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|
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|
|
|
|
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|
|
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|
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|
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|
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|
|
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|
|
|
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sio-1
|
|
|
|
IC 2402
|
|
|
|
20,000
|
|
|
|
0844+31
|
|
|
|
70*
|
|
|
|
18.0
|
|
|
|
1.83
|
|
|
|
~io-<
|
|
|
|
0924+30
|
|
|
|
8,000
|
|
|
|
Compact
|
|
|
|
497*
|
|
|
|
21.5
|
|
|
|
Source
|
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|
2.02
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|
|
|
-10-'
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|
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|
*Distance from galaxy; quasar is much closer to hot spot or radio lobe.
|
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|
Appendix to Chapter 3
|
|
1971, Arp, H., Astrophys. Letters, 9, p. 1. The original picture of the connection between Markarian 205 and NGC 4319 was published here (Fig. 3-1 in the
|
|
present book). The object was also discussed in the "Redshift Controversy" (loc. cit. Chap. 1) and in following references:
|
|
1972, Lynds, R. and Millikan, A. G., Astrophys. Journ. (Letters), 176, p. L5. 1979, Stockton, A., Wyckoff. S., and Wehinger, P., Astrophys. Journ., 231, p. 673. 1981, Wyckoff, S. and Wehinger, P. A., Sky and Telescope, 61, p. 200 (March 1981).
|
|
The connection is conspicuous in pseudo-color in this last publication, even while the authors state that they have established beyond any doubt that Markarian 205 is ten times more distant!
|
|
1983, Sulentic, J. W., Astrophys. Journ. (Letters), 265, p. L49. This is the image processing work that confirmed the broad connection (Fig. 3-2) and discovered the sinuous connection back to NGC 4319 discussed in this chapter.
|
|
1984, Kunth, D. and Bergeron J., Mon. Not. Roy. Astron. Soc, 210, p. 873. The subject of this paper is the strong sodium absorption in the spectrum of the quasar, PKS 1327-206 due to the adja-
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|
cent peculiar galaxy. When examined on cataloged photographs, the system appears connected as shown in Figure 3-5. 1976 "Paris Conference" IAU Colloque No. 37—Decalages vers le rouge et 1' expansion de l'univers,—eds. C. Balkowski and B. E. Westerlund (Paris Centre National de la Recherche Scientifique Colloques Internationaux No. 263), p. 377 and other articles.
|
|
Because part of the subject of this conference was anomalous redshift, the International Astronomical Union (IAU) did not want it to be at the elevated status of a symposium. Only with pressure from some French astronomers was it able to go forward and then as a colloquium only. Nevertheless, the conference produced the best summary of anomalous redshift data to that date, by a number of contributors, and should have established beyond doubt the existence of these effects.
|
|
Quasars Visibly Connected 45
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|
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1977, Kronberg, P., Burbidge, E. M., Smith, H. E., and Strom, R. G., Astrophys. Journ. 218, p. 8. This paper discusses the relation of the quasar and the ultraviolet objects to the radio galaxy 3C 303.
|
|
1974, Grueff, G. and Vigotti, H., Astron. and Astrophys., 35, p. 491. 1977, van Breugel, W.J.M. and Miley, G.K., Nature, 265, p. 315. 1980, van Breugel, W.J.M., Astron. and Astrophys., 81, p. 275.
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|
All these papers discuss the radio jet galaxy, 0844 + 31. 1975, Ekers, R., Fanti, R., Lari, C , and Ulrich, M.-H., Nature, 258, p. 584.
|
|
This paper reports the alignment of compact radio sources and lobes across the galaxy in the radio source B2 0924 + 30.
|
|
46 Quasars Visibly Connected
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CERTAIN 4 GALAXIES WITH MANY QUASARS
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If a few quasars belong to some nearby galaxies, where do the majority of quasars belong? Over three thousand quasars are known now; most of them are spread over large areas of the sky where it is not immediately apparent that they are associated with any particular galaxy. One obvious answer might be, for example, that most quasars were ejected away from their galaxies of origin to mingle somewhere in intergalactic space. Perhaps only a few have been ejected so weakly that they orbit around their galaxy of origin. Perhaps only a few are seen close to the moment of their emergence, where they still show an umbilical attachment to their parent galaxy. But it is possible that sometimes a galaxy might eject many quasars and might be caught in the act of doing this. Could it have been predicted that some galaxies had many associated quasars? If so, it also might have been predicted that they would be encountered unexpectedly.
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A. The Galaxy with the Longest Known Optical Jets, NGC 1097
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In 1974, I was sitting at a viewing machine in Edinburgh, systematically scanning
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deep plates of the southern sky taken with the Schmidt telescope in Australia. This was part of a more than ten-year project with Barry Madore that culminated with the publication in 1987 of a two-volume Catalog of Southern Peculiar Galaxies and Associations. Someone from the Schmidt Telescope Unit brought me a deep plate of another region.
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"Do you see this faint marking pointing at this galaxy?" he asked.
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"Well, yes, I see it, but it does not look like features which I've had previous experience with, so I would guess it was not real."
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I had made the typical response of the expert and was soon proved to be totally wrong. The discoverers of the jet, R. D. Wolstencroft and W. Zealy, obtained additional independent photographs and proved it was a luminous jet emerging from the galaxy. Their discovery turned out to be the most spectacular example of optical jets found to date.
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No one yet has the slightest idea what mysterious process may have caused them.
|
|
About one year later, I had a dark-of-themoon run of about 14 nights in the prime focus cage of the new 4-meter reflector on Cerro Tololo in Chile. The telescope was not
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Certain Galaxies with Many Quasars 47
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yet commissioned but the director, Victor Blanco, had invited me to test it photographically on objects of particular interest. In this exceptional observing opportunity, one of the objects which had my top priority was the jet galaxy, NGC 1097. From the many limiting photographs that I obtained of the object, Jean Lorre performed a masterful image-processing job. He information-added all the plates, stretched the contrast at the low surface brightness of the jets, and removed all but the largest stars by replacing them with adjacent sky averages. The final, best picture obtained of the jets coming from NGC 1097 is shown in Figure 4-1.
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The image processing has brought out the fact that the narrowest jet, proceeding slightly east of north in Figure 4-1 ends in a "puff of faintly luminous material. Directly opposite, emerging from of the other side of the galaxy, is a fainter, redder jet, which is clearly the counter-jet to the first. An extremely long, straight jet extends very faintly down to the southwest from the body of the galaxy. It is not quite exactly opposite the fa-
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figure 4-1. The spiral galaxy NGC 1097 and its /our optical jets. Photographs by Hakon Arp, image-processed by Jean Lone.
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mous "dog-leg" jet which points off toward the northeast. The sudden right-angle turn made at the end of the dog-leg jet has always defied explanation. If it is a secondary ejection, there is no apparent reason why it should make so closely a right-angle bend. Surprisingly, the jets have never been clearly detected in radio emission, not even with the Very Large Array (VLA) radio telescope. There are some slightly higher surface brightness spots in the dog-leg jet which I have measured spectroscopically, but only a very faint, featureless continuum registers, telling us very little about the nature of the condensations.
|
|
Detailed photography of the interior of the galaxy reveals a beautiful, two-armed barred spiral. The nuclear region contains unusually large, bright clumps of emission. The galaxy is one of a small group called "hot spot" nucleus galaxies. As accurately as can be determined, the jets emerge directly from the small central nucleus. Figure 4-2 shows the narrow spiral arms delicately outlined by gaseous emission (H II regions). That photo-
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48 Certain Galaxies with Many Quasars
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JET 3 Figure 4-2. Pnologroph in light of hyirogen emission (Ha) showing spiral arms in the interior of N G C 1097, and rupture of the arm as jet I] passes through the north arm. Photographs used in this and preceding figure were talcen with the CTIO 4-meter telescope (National Optical Astronomj Observatories, operated by the Association of Universities for Research in Astronomj, Inc., under contract with the National Science Foundation).
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|
|
graph also shows the exciting result that the spiral arm is clearly disrupted just ahead of where the narrowest jet passes out to the north-northeast: We can actually see the physical effects of this jet punching through the spiral arm!
|
|
Moreover, because we know the approximate rotation velocity of NGC 1097, we can compute, from the distance that the punctured point on the arm has moved forward, how long ago the event happened. The rotating spiral galaxy is like a great clock in the sky, and although we do not know what has been shot out of the center, we can gather a very good estimate how long ago it happened. The answer comes out that the event is only about 107 years old. Ten million years
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|
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|
is a short time on the scale of the Universe. It is only about one-thirtieth of the time needed for one rotation of a spiral galaxy. I believe these kinds of estimates are the only reliable estimate of the age of whatever it is that has been ejected out of the nucleus of the galaxy. We will see this estimated age of a few times 10' years reappearing in other systems to follow. This will become an important datum when we later try to deduce the nature of the ejected material.
|
|
It is also interesting to note that with the jets already so faint at such an early age, the implication is that such phenomena are very transitory, so that we should not see many galaxies in such a stage. Moreover, we apparently see these ejecta because the expulsion
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Certain Galaxies with Many Quasars 49
|
|
|
|
has gone off in the plane of the galaxy. If many galaxies ejected nonluminous material out of their planes, there could be enormous numbers of similar ejections of which we are completely unaware. Does expulsion in the plane slow the ejecta down so that they remain closer to their galaxy of origin? In Figure 4-2, we see an anomalously large H II region just at the rupture point of the northern arm. Could this somehow be connected with the ejection event? If the ultraviolet object in NGC 4319, which is opposite to Markarian 205 (see Chapter 3), is gaseous emission, could it be related to a similar ejection in the plane? It is amazing that no astronomers are following up these important clues.
|
|
The next lurch forward in the study of NGC 1097 was again fortuitous. The object was observed in X-ray wavelengths by the Einstein satellite in January 1979. Eventually it was noticed that there was a lot of X-ray emission on the north side of NGC 1097. Wolstencroft pointed out to me that one Xray source coincides with a star brighter than 18th magnitude. I opined that this was too bright to be a quasar, but when I took the spectrum, I was wrong again. It was a quasar of redshift z = 1.00. Wolstencroft obtained objective-prism plates of the area and we looked around for emission objects. We found six quasars, all in a small area near the northern jets. This corresponded to an over-density from the expected background by a factor of 25. Note that here again we find an over-density of almost exactly the amount found around the galaxies discussed in Chapter 2. The only encouragement we received that this was a significant result was when we encountered great difficulty in getting it published.
|
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It was clear that the situation required another heroic effort to achieve resolution. With a program that was to take three collaborators more than three years we set out to answer the questions: (1) Is the enhanced quasar density present only in the area near
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|
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the northern jets, or is it more generally present over the area around NGC 1097? (2) With a complete search of a large field around NGC 1097, would the edges of the field approach the background density of quasars found in other parts of the sky?
|
|
Good-seeing objective-prism plates were obtained from the Schmidt telescope in Australia. The Chinese astronomer X. T. He, searched and researched these plates, eventually producing a list of 43 candidates within the central 8.1 square degrees. I measured 33 of these candidates spectroscopically with Carnegie Institution's telescope in Chile. They turned out to be 94% true quasars, the best percentage average for picking quasars I have ever seen. We assume that essentially the whole of the candidate list are quasars and plot their distribution in Figure 4-3.
|
|
Figure 4-3 tells the story at a glance. The concentration of quasars toward NGC 1097 is obvious. In addition, the quasar density at the edges of the field drops to just the value expected for an average sky. In order to make the quasar concentration go away, one would have had to miss about 60 quasars in the field, an obviously impossible number. But, of course, finding more quasars in this field would then raise the already significant excess-density of quasars to even larger values.
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This result clearly puts the ball in the establishment's court. The return strokes, however, have been less than brilliant. When I showed these results at the Liege Symposium in 1983, everyman's friendly radio astronomer approached me with his usual exquisite blend of pomposity and ineptitude and said, "That's obviously a statistical fluctuation."
|
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After three years of hard work and big telescope time, an anonymous referee reported that the paper "was not in a suitable form for publication." The editor was prepared to allow the referee an open-ended era in which to pursue this opinion but my collaborator, Wolstencroft, produced six pages of closely written statistical computations with
|
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|
50 Certain Galaxies with Many Quasars
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|
I Dec.
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|
-29°
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|
1 '
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|
•19
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EJ
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33»30
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•17
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-31°
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26.24 15*15
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|
|
02 40 R.A.
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|
|
|
figure 4-3. Plot o/all quasar candidates (94% prove to be quasars) around NGC 1097. From ArJ>, Wolstencro/t, and He.
|
|
|
|
the result that the paper was eventually published after a delay of only one year and three months.
|
|
Certain significant aspects of the NGC 1097 situation, however, serve to introduce the next result in this chapter: (1) The radio emission in NGC 1097 occurs asymmetrically placed over on the side of the strong northern jets. (2) The X-ray emission is asymmetrical, likewise on the side of the northern jets (both the inner and outer X-ray emission). (3) The quasars are preferentially aligned with the jets, more of them being on the side of the northern jets. These latter points are illustrated in Figures 4-4, 4-5, and 4-6.
|
|
These are extraordinarily important points because they make clear that the radio and inner X-ray material is associated with the galaxy. Since the quasars are associated with the outer X-ray material, which is con-
|
|
|
|
tinuous with the inner, and since the quasars are also aligned with the jets, this shows that the association of the quasars cannot be coincidental. It must have some physical significance. Specifically, these results imply that the X-ray material, radio material, and quasars are all part of the ejection which is marked by the optical jets.
|
|
Do other examples exist to support this picture?
|
|
B. The Disturbed Galaxy NGC 520
|
|
The first chapter of this book describes how, in looking around galaxies in the Atlas of Peculiar Galaxies, I found apparently associated radio sources and quasars. In order to amplify this point a little here, I should say that these associations were mostly with numbers 100 to 160 in the Atlas. Those categories
|
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|
Certain Galaxies with Many Quasars 51
|
|
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|
JET 2 10'-
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|
•30° 30'
|
|
|
|
DET1
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|
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Figure 4-4. XTOJ and radio maps o / N G C 1097. Note quasars 1 tnrougn 6 (X symbols) coincide uiit/i man> of the patches o/X-ray emission. Placement of jets and then extensions indicated by full and dashed tines.
|
|
52 Certain Galaxies with Many Quasars
|
|
|
|
12
|
|
in
|
|
UJ CD
|
|
|
|
ols_i
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(20
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|
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|
|
POSITION ANGLE FROM NGC 1097 (DEG.)
|
|
|
|
Figure 4-5. The alignment of the direction of all the quasars (filled points) with the direction of the jets in N G C 1097. From Arf>, Wolstencro/t, and He.
|
|
|
|
X-RAY EMISSION AROUND NGC 1097
|
|
|
|
1.5 HARDNESS RATIO
|
|
0.5
|
|
|
|
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|
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|
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6
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|
DISTANCE IN ARC HIN
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20
|
|
|
|
INNER 32 TO 64 ARC SEC
|
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120
|
|
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|
360
|
|
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|
COUNTS
|
|
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40
|
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20
|
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|
INNER 64 TO 90 ARC SEC
|
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|
120
|
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|
360
|
|
|
|
POSITION ANGLE
|
|
|
|
Figure 4-6- These plots demonstrate continuity of high energy to low energy ratio in X-ray sources outward from center of N G C 1097. Also peaks of inner X-rays in direction of strongest jet (pos. angle n'360°). Calculations from Wolsttncro/t.
|
|
|
|
Certain Galaxies with Many Quasars 53
|
|
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|
QUASARS
|
|
|
|
QUASARS
|
|
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|
Figure 4-7. The disturbed galaxy NGC 520. It is number 157 in the Atlas of Peculiar Galaxies. Directions of cone of radio sources discovered in 1967 and lines of quasars discovered in 1970 and 1985 are marhtd.
|
|
|
|
in the Atlas represent the most chaotic and disturbed objects, presumably contorted by inner activity and explosions. Galaxies in categories with much higher and lower numbers represented a selection of interacting doubles, dwarfs, and other peculiar objects which one would not expect to show violent activity. Thus a significant point, which most critics insisted on overlooking, was that the associations of sources turned out to be primarily with these central numbers in the Atlas.
|
|
One of the most disturbed objects in the entire Atlas is number 157. It is shown here in Figure 4-7. In 1967, I knew of no quasars around it. I did, however, notice an unusual number of radio sources which appeared to define directions of ejection to the northeast and southwest. Three years later, in 1970, I became aware of four radio-loud quasars to
|
|
|
|
the southwest. They defined an almost perfect straight line pointing back toward NGC 520. The properties of the quasars in this line resemble each other in a number of ways such that the overall probability of such a chance configuration is less than one in a million. The line of quasars also lies within the previously defined direction of radio source ejection. The line is shown in Figure 4-8.
|
|
I remember showing this line of quasars to John Bolton in 1970. As one of the founders of radio astronomy, John has made many identifications of radio sources with quasars over the sky. He said he had not seen any so straight but had seen many approximate lines and apparent chains. It seems amaiing that until very recently no one has systematically investigated these features. I suppose the reason is that the configurations involve quasars
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54 Certain Galaxies with Many Quasars
|
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1
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Figure 4-8. A plot o/strongest radio quasars in a larger area around N G C 520. Redshifu are written next to symbols.
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28m
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|
of different redshift. (Recently, tentative alignment results for
|
|
faint quasars were put forward in the literature with great difficulty by Clube and Trew, Liege Conference, p. 374 and Monthly Notices of the Royal Astronomical Society, submitted.)
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Again the investigation of NGC 520 languished, this time for about 10 years, until 1980. By that time, I had started finding quasars over homogeneously searched areas of the sky by using the ultraviolet-excess techniques described in Chapter 2. Jean-Pierre Swings and Jean Surdej of the Institut d'Astrophysique in Liege, Belgium, joined me in a collaborative project of searching several areas of about 20 square degrees each on the sky. I had already obtained plates covering the NGC 520 region but here was an opportunity to have the quasar candidates surveyed by astronomers without previous experience with the region, who would therefore be unbiased.
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Over the next few years I measured their candidates with the Carnegie telescope in Chile. The most conspicuous feature in the whole field turned out to be a line of quasars going through NGC 520! In order to make
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absolutely sure of this result, I then asked Oscar Duhalde of the Las Campanas Observatory to take an ultraviolet/blue plate on a completely different telescope and the two of us examined independently the 2.1-squaredegree field which had been studied around NGC 520. The original search went to 20th apparent magnitude, but to be on the safe side for completeness, we restricted ourselves to quasars brighter than 19th magnitude. Seven quasars resulted from the Swings/Surdej candidates, five on the line and two off. Six additional quasars were found by Arp/Duhalde, one on the line and five off. Swings and Surdej originally were enthusiastic about the line, but after the Liege Conference in 1983, they renounced it, claiming that the association had been found from the Arp/Duhalde search!! The quasars found in this double-independent search of the area around NGC 520 are shown in Figure 4-9 where the reader will have to judge for himself the significance of the line.
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It is important to realize that just the distributed quasar density near NGC 520 is, by itself, much higher than in the expected
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Certain Galaxies with Many Quasars 55
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Figure 4-9. All quasars brighter than 19th apparent magnitude around N G C 520 are shown, from two independent searches within the pictured area (from Arp and Duholde 1985). Is there a line of quasars going through N G C 520! Why did referees and editors of two major journals refuse publication of this result!
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background. It reaches 15 times expected density, about the same factor that we have encountered for excess density around galaxies previously discussed. Since all members of the line are undeniably quasars, in order to make the line "go away," one would have to discover many more quasars which would further increase the density above its already strong excess.
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The next piece of the puzzle fell in place, as the X-ray astronomers would say, serendipitously. I was scanning a list of targets which the Einstein X-ray observatory had observed. There, amongst a study entitled, "Normal Galaxies," was my old friend, NGC 520. How anyone could call NGC 520 a normal galaxy passes all understanding. But I understood
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somewhat after I wrote the Harvard/Smithsonian Center to try to get a copy of the observations. It turned out they had been made by a new acquaintance, an astronomer who had just advanced his career with an article in the magazine called The Sciences, in which he had dismissed as trash anything I had ever uttered about redshifts. You can imagine that getting my hands on this X-ray map was not easy. I have never been able to compare it with other fields taken under the same conditions. But the single map I did get showed a lot of Xray emission from the vicinity of NGC 520. It was apparent that whatever is producing the X-rays is elongated more or less along the line of the quasars. Figure 4-10 shows that the direction of the radio emission designated in
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56 Certain Galaxies with Many Quasars
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RADIO SOURCESO967)
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m
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UJ
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X-RAY EMISSION
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CD
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23' < r<37'
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OPTICAL QUASARS(1983)
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RADIO QUASARS(1970)
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a:
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1 2UJ
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QUASARS r<36'
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Figure 4-10. The directions on the sky, from N G C 520, of the radio
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sources discovered in 1967, and
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the quasars discovered in 1970
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(arrows). The X-raj material and
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additional quasars discovered in
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40
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120
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200
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280
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3 6 0 1983 are rej>resented try upper and
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POSITION ANGLE FROM NGC 520
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lower histograms respectively.
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1967 coincides very closely with the direction of the radio quasar line discovered in 1970, which then coincides with the direction of the quasar line discovered in 1983, which in turn coincides with the peak direction of Xray emission discovered in 1983.
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As in the previous case of NGC 1097, we have in NGC 520 strong evidence for quasars ejected in a jet and counterjet direction and for this ejection to be accompanied by X-ray and radio material. In NGC 520, no optical jets are visible, but on the other hand, the galaxy is much more explosively torn up than NGC 1097, suggesting a very violent event.
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As to the interpretation of the structural appearance of NGC 520, there has been quite a fad in recent years to explain all asymmetrical galaxy forms as collisions or mergers. NGC 520 was interpreted in this fashion by my friends Alan Stockton and Francesco Bertola. The Armenian radio-astronomer Tovmassian, however, finds a single, compact
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radio source in the center of NGC 520 and favors the exploding-galaxy interpretation. My opinion is that the photographs taken with high-resolution telelscopes do not permit the interpretation of NGC 520 as two galaxies. Finally, the radio, X-ray, and quasar activity we have just discussed supports the interpretation of NGC 520 as an active galaxy.
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Two things have always bothered me about NGC 520. One is the large scale of the activity—the straight line of radio quasars stretches up to 7 degrees away from the galaxy—and the second is the relatively bright apparent-magnitudes of the quasars. The redshift of NGC 520 is about czo = 2272 km s"1, which, on the cosmological hypothesis, gives a distance about twice as great as the Virgo supercluster center. I have occasionally had a little thought: Is NGC 520 really this distant or it is closer than its redshift would indicate? In Chapter 5, we see the most recent evidence that the galaxy may be closer.
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Certain Galaxies with Many Quasars 57
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Figure 4-11. The /ilaments emitting light from gaseous hydrogen-alpha are shown in this picture of M82, photographed by Allan Sandage.
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C. The Exploding Galaxy M82
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This galaxy has always been one of the brightest and most peculiar known. (M stands for Charles Messier, the 18th century comet hunter.) In 1963, Allan Sandage took photographs of M82 revealing a twisted set of emission filaments emerging from either pole. M82 was interpreted as an exploding galaxy and became a prototype for objects in the universe exhibiting violent activity. (Some years later, there was an attempt to interpret M82 as a normal galaxy drifting through a cloud of dust, but in my opinion, the photographs patently rule that out. In addition, velocity spreads were later found in the gaseous filaments.) Sandage's photograph is shown in Figure 4-11.
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We will come back to M82 in later chapters because it is such a key object. But for the present it suffices to say that the galaxy is a companion to M81, an even larger, apparently normal spiral which dominates the M81 group of galaxies. From the results of finding quasars near companion galaxies described in Chapter 2, I was predicting that quasars should be found near companions like M82. The system lay in a direction passing too near our own galactic plane, and hence was too crowded with stars for me to use the ultraviolet-excess technique for quasar-discovery. But about this time, Arthur Hoag had invented the grism (grating prism) which would give small spectra of faint objects in a field. Because Art had been a long and valued friend, I urged him to search for quasars around companion galaxies such as
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58 Certain Galaxies with Many Quasars
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Figure 4-12. The four quasars which have been discovered near M82 are circled. The photograph is oxygen emission, showing
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the asymetricai/foments which appear to be associated with the explosion. A radio source (slightly extended contours) appears
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to have been ejected along with the quasars from the "notch" in the southeast side of M82.
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M82. I must say, the prospect of one of the sars back to an origin in M82. As Figure 4-12
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genuinely good guys in astronomy making an shows, they can be all contained within a
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important discovery with his genuinely impor- cone emerging from the center of the galaxy.
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tant instrument pleased me also. But he in- The opening angle of this cone is just about
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sisted on observing so-called blank fields on the observed opening angle on the ejection
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the usual idea that this would give us the num- cones that we have seen emerging from NGC
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ber density of quasars at the edge of the uni- 1097 and NGC 520. Moreover, in M82, this
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verse. (When it comes to the universe, one ejection cone emerges from the galaxy on the
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edge is about as good as another, hence the same side as the puff of forbidden oxygen
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blank fields.) He was observing with Sandage emission. In fact, on the northern side of the
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one night and ran out of objects at the end of [O II] emission there is a notch cut out, into
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the night. To fill the time, they took a plate of which the orgin of the ejection cone natu-
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M82. Can you imagine, they found three qua- rally fits. Finally, if we look back at Sandage's
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sars about a galaxy diameter away to the south- original hydrogen-alpha picture in Figure 4-
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east, an order of magnitude closer to each 11, we see that the most conspicuous absorp-
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other than expected and all of about the same tion feature in the galaxy goes directly back
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redshift!
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to the center along the line of this postulated
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Of all the quasars known, this is a unique grouping. It could hardly be a coincidence
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ejection cone (see also Arp 1980 in references in Appendix to this chapter).
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that they fall so close to the unique galaxy
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The most recent developments concern-
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M82. It is natural, therefore, to trace the qua- ing this system again come from X-rays. Fig-
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Certain Galaxies with Many Quasars 59
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M82
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X-RAY MAP
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69°55'20'
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1
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/ - 69°55'00" —
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i
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9
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QUASARS 69°54'20"
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o
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9h5f45s
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40s
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35s
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RIGHT ASCENSION
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Figure 4-13. The radio map (photographed) o / M 8 2 , with line contours o/X-ray emission superposed. From Kronberg, Bier-
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mann, and Schwab. See chapter 9 for further discussion of X-ray emission.
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ure 4-13 shows an X-ray map superposed on a be related to any other unorthodox results
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radio map of the system. The compact, varia- which had been previously known. But, as Fig-
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ble radio sources in a line down the spine of ure 4-12 shows, the patch of radio emission fits
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the galaxy are very peculiar, but the most sig- exactly into the quasar ejection cone just as it
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nificant result for our purposes is that the X- emerges from the explosive center of M82.
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ray material is again over on the southeast side of M82 and, in fact, extends out generally along the direction of the ejection cone which we had identified several years previously from the quasar and morphological data. Added to the association evidence for the quasars, this correspondence of detailed X-ray and morphological evidence with the quasar alignment would indicate in this one case alone that the association of the quasars cannot be accidental.
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To summarize the results of this chapter, I would say that we have analyzed over many years and in great detail, three of the galaxies with the best evidence for explosive, ejecting behavior. In each of these cases we have found very strong statistical evidence for density enhancements of quasars near these galaxies. In all three cases alignments of quasars towards the centers of these disturbed galaxies exist that can hardly have occurred by chance. Connected with these alignments we find evi-
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Radio ejection? Of course. When J. J. Condon was observing a number of bright galaxies with the Very Large Array telescope, he found an unusual radio source just to the southeast of M82. As is customary in extragalactic astronomy, this observation would not
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dence for ejection of radio material and X-ray material. There does not seem to me to be much doubt, in just these cases alone, and even without the evidence from the first three chapters, that quasars arise from some kind of ejection process within galaxies.
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60 Certain Galaxies with Many Quasars
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Appendix to Chapter 4
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1984, Arp. H., Wolstencroft, R. D., and He, X. T. Astrophys. Journ., 285. p. 44. This is the latest paper on NGC 1097 and contains references to earlier work. NGC 1097 is also discussed below.
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1983, Arp, H. in "Liege Symposium on Quasars and Gravitational Lenses," Institut d'Astrophysique. Universite de Liege, June 1983, Paper 47.
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A number of results on "Groups, Concentrations, and Associations of Quasars," appear in the proceedings of this conference which are not published elsewhere. Discussion recorded at the end of this paper includes some obviously inaccurate statements about quasars of redshift near z = 1 containing only one visible emission line in their spectrum and selection of quasars near NGC 520. 1980, Arp, H., Annals of the New York Academy of Science, Vol. 336, pages 94-112.
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This is the "Texas Symposium" in Munich. Results for association of quasars with galaxies, particularly with companion galaxies, are reviewed to that date. The evidence for an ejection cone of quasars from M82 is discussed only in this publication. The fourth quasar southeast of M82 is shown in Astrophys Joum., 271, p. 479. 1983, Condon, J.J., Astrophys. Journ., Supp., 53, p. 459.
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Radio observations of M82. 1985, Arp, H. and Duhalde, O., Publ. Astron. Soc. Pac, 97, p. 1149.
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Observations of quasars near NGC 520.
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Certain Galaxies with Many Quasars 61
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DISTRIBUTION 5 OF QUASARS IN SPACE
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The conventional view of quasars is that they are normal galaxies which have, for some reason, superluminous nuclei which enable them to be seen at great distances in the universe. But if quasars really were these kinds of galaxies, we should expect to see them clumping into the clusters or superclusters that characterize the distribution of galaxies on the largest scales. Attempts have been made to relate some quasars with faint, adjacent galaxies of the same redshift. But no conspicuous clusters are evident. Moreover, it is completely clear that we do not see clusters or groups of quasars all having closely the same redshift. The conclusion forced on the conventional believers is that quasars are so rare that we seldom see a cluster of galaxies with one; that is, far less than one quasar exists per average supercluster.
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But if we look around the quasars we do see, to a faint enough level, we should see the galaxies that accompany them in their clusters and superclusters. Wide-field Schmidt telescopes, since the invention of high-detectivity emulsions, can routinely register galaxies to a limiting apparent magnitude fainter than 23. That corresponds to a redshift for a
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normal galaxy of at least z = 0 . 5 . We should be able to easily see faint, rich
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clusters of galaxies around quasars out to this redshift and beyond. We do not. (You can believe that if we did we would have heard an enormous amount about it!) Clearly, this is an outstanding violation of the cosmological assumptions.
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The only way to place the quasars into clusters, where they "belong", is to move them in much closer than their redshift distance. In fact, throughout this book we shall see that if the objects with anomalous redshifts are assigned closer distances they join nearby groups and clusters of galaxies. This is the way the universe is observed to be structured. But if these objects are left out at their putative redshift distances they are left hanging isolated in space.
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Of course an inverse investigation could be made. The faintest, richest superclusters in the sky could be identified and the area which they define summed. On the cosmological assumption these areas should contain most of the known quasars of the same redshift. My impression, from what I have seen of the distribution of faint galaxies with re-
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Distribution of Quasars in Space 63
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TABLE 5-1 Quasars in Dense Groups
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No. Group Name
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1. Hazard 1146+ 1112 (~2°SEof NGC3810)
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2. NGC 450 SW (-2° SW of NGC 450)
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3. NGC 2639 SE (~30'SEof NGC 2639)
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4. NGC 1097 NE (within 24' of NGC 1097)
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5. NGC 520 (within 28' of NGC 520)
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z. 1.01 0.955 1.18 3.1 0.33
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Redshifts of Quasars
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Z;
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Zj
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Z<
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Z5
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1.01
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1.10
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0.86
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2.12
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0.960 0.69
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1.23
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1.89
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1.11
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1.52 (0.78)
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0.53
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1.00
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0.34
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0.89
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0.92
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1.20
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0.63
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1.41
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Factor of
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Density
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Area Over
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It,
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(sq. deg.) Average
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0.014
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60
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0.013
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64
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0.013
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51
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(1.1) 0.04-0.02 21-50
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1.47
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0.05
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60
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spect to quasars, is that this test would fail spectacularly and that this is why the researchers of cosmological persuasion have not performed it.
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On the other hand, examining the distribution of quasars on the sky does reveal conspicuous clumps and groups of quasars. The trouble is that the quasars within each group have dissimilar, or only moderately similar, redshifts. If thes< groupings are real, and if the redshifts were distance indicators, each group, with its range of redshift, would represent an elongated "finger" of quasars pointing just at our position in space. The Copernican principle, namely that the odds are overwhelmingly against our occupying a special position in the universe, would then require that the redshifts of these quasars did not indicate their distances. The fingers pointing at us are telling us our assumptions about redshift are foolish.
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A. The Densest Groups
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of Quasars
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In order to investigate this question of grouping of quasars without prejudice as to redshift, I list in Table 5-1 the densest groups of four or more quasars that I have encountered in my 20 years of quasar research. Some of these groups, such as the ones shown in Figures 5-1 and 5-2 are so compact and isolated that there could be no question that they are a physically associated group of quasars. I make no attempt to prove this statistically in the sense of computing the chance of finding these configurations in a sample of random quasars in the sky. Since most astronomers pay no attention to proofs that quasars are local anyway, I might as well present an easy proof rather than a hard one. Instead of doing complicated statistics on heterogeneous searches, I simply reason that if the five dens-
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64 Distribution of Quasars in Space
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N' .
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. 10'
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Figure 5-1. laenti/icanon of all quasars mthin an area heated about 2° SE o/NGC 3810, found from objective-prism spectral searches bj Arp and Hazard. Redshifu are written next to position of quasars.
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NGC 4 5 0 SW
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-2°/30' DEC
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3'/OO'
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Figure 5-2. A plot of all quasars found within an area southwest of N G C 450 searcKed for ultTavioletexcess candidates by Surdej, Swings, and Arp.
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20 -
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Radio quasars
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V>18.0
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—
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Densest groups V2:18
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-
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.8 1.2 1.6 2.0 2A
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2.8 3.2
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figure 5-3. The distribution of quasar redshifts for the densest groups compared to the distribution of redshifts for radio quasars from all over the sky.
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est groups in Table 5-1 were random associations, they should have the same properties as the average quasars in the sky. They have, in fact, outstandingly different properties. For example, Figure 5-3 and Table 5-1 reveal that there is a clear preference for redshifts between 0.8 < z < 1.2, whereas radio quasars from all over the sky are rather evenly distributed between 0.4 < z < 2.2.
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There is also a tendency to find pairs of quasars within each group. (Pairing tendencies for quasars are discussed further in the Appendix to this chapter.) On the average, the pairs within these dense groups are separated by only 4.6 arcmin on the sky and only
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0.07 in redshift. The chance of finding such pairs by chance within the general population of quasars is only about 10~3 per pair. Yet we find eight such pairs in the five dense groups. Even allowing for the fact that these are selected dense groupings of quasars, there is clearly a significant physical association of pairs. Their average difference in redshift of A z = 0.07, however, translates to a velocity difference of 21,000 km s'1, a clearly impossible value for objects belonging, on the cosmological interpretation, to the same cluster or supercluster of galaxies*
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The physical reality of these dense groups destroys the possibility that quasars are at
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T h e one pair among the 26 quasars listed in Table 5-1 which has very closely similar redshifts was recently pounced upon by advocates of conventional quasar distances. They proclaimed this pair to be the result of a gravitational lens of enormous and unprecedented mass sitting invisibly out somewhere in this direction in the universe (Nature 321, p. 142, 1986). Embarrassingly enough, further observations revealed almost immediately that the spectra were in fact enough different so that the quasars had to be two separate, albeit quite similar quasars. This is just the pairing tendency evidennt in the quasars discussed in this chapter and evident in the compact, excess-redshift ejecta of active galaxies discussed in following chapters. The above, widely publicized incident of marvelous discovery and almost instant refutation, however, underscores two points: (1) no result in the field is absurd enough to provoke reexamination of basic assumptions, and (2) selecting one aspect of data which supports a hypothesis and ignoring other aspects which contradict that hypothesis is a form of "altering data".
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66 Distribution of Quasars in Space
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their redshift distances, because, as just ex- optically faint radio quasars in the North Ga-
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plained, the redshift range of the associated lactic Hemisphere (NGH radio quasars in Fig.
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quasars is too large by a wide margin. A typi- 5-4) are associated with the Virgo cluster of
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cal cluster of galaxies near redshift z = 1 galaxies, i.e., the center of our Local Super-
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would have redshifts ranging, at most, be- cluster. This 1970 study is now translated into
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tween 0.99 < z < 1.01.
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the upper-left panel in Figure 5-4 where we
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But at the same time, the existence of these see that the brightest quasars belonging to the
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groups is the key that unlocks a more detailed Virgo cluster are concentrated in redshift
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understanding of the puzzling data on quasars. near z ~ 1. There are almost no quasars near z
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The reason that it is such a key is that it al- ~ 2. Presumably, they are too faint in appar-
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lows us to ask a crucial question. (It might be ent magnitude to be observed in Virgo!
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said that the most difficult part of research is
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In contrast, the same sample of quasars in
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not to get the right answer, but to ask the the opposite direction of the sky (SGH radio
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right question.) The question is:
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quasars) show a strong concentration near re-
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"Why do the densest groups of quasars have dshifts z ~ 2. This represents gross differences
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redshifts near z = 1?"
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in the quasar distribution within a complete
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and homogeneous quasar sample over the sky.
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B. The Intrinsic Luminosities of Quasars of Different Redshifts
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On the cosmological interpretation of quasars this would require an enormous violation of the usually assumed cosmological principle
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One obvious answer to the question of why the densest groups of quasars have z ~ 1 is: "The luminosity of quasars with z = 1 is greater than the luminosity of quasars of other redshifts." In that case, the z = 1 qua-
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that on large distance scale the universe is homogeneous. It is astonishing that this clear evidence contradicting the cosmological assumption has lain ignored and uninvestigated for over 15 years!
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sars could be seen at a greater distance, where
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To return to the luminosity-redshift rela-
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the scale of their separation appears smaller tion for quasars, we can easily draw in the line
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and the groups therefore appear denser.
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satisfying the average values for the NGH ra-
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Can this be tested? Yes, a straightforward dio quasars in Figure 5-4. This "roof-shaped"
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way to test this is by plotting the apparent relation is shown as a line in the two panels
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magnitudes versus the redshifts for all the var- in the middle of the figure. Even though this
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ious groups of quasars that I have, over the roof-shaped line is derived from the NGH
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years, come to believe are physically associ- quasars in the upper-left-hand panel, we do
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ated. This has been done in Figure 5-4. For not draw it in that panel in order to avoid
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these quasars at the same distance, those of prejudicing the eye with the line. One can
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brightest apparent magnitude must be the thereby see that the points just representing
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most intrinsically luminous. We realize from the NGH quasars by themselves clearly de-
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the upper-left-hand panel alone in Figure 5-4 fine the adopted relation. (A roof-shaped rela-
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what we should have seen in 1970, that the tion implies that the quasars with redshift z ~
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quasars near z = 1 are the intrinsically bright- 1 are the intrinsically most luminous and that
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est quasars. (Actually, this point was first quasars with both lower and higher redshifts
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stressed in my contribution to the 1972 Kra- are less luminous.)
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kow and Australian symposia referenced in
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The fit of this luminosity-redshift relation
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the Appendix of Chapter 2.) In that same to the quasars studied in the NGC 1097 field
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Chapter 2, we discussed the 1970 paper in the is shown in the upper middle panel of Figure
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Astronomical Journal which showed that the 5-4. From the study of NGC 1097 discussed
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Distribution of Quasars in Space 67
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17
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V mag. -
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19
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I
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3° $* °e°
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° oo° ° o
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°
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°o
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o
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I
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NGH
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RADIO aUASARS_
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o
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_ o
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21
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17 - . • • V mag.
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*./
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I I
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I I
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I I
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SGH
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RADIO
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. aUASARS
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• '
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19
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_
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+
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NGC 1097
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+
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-
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N \
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+ \ +
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—
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SCULPTOR AREA
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i
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r
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NGC 520 17
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K XX
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19
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21
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DENSE
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GROUPS 17
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o+
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21
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1
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2
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z
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Figure 5-4. The apparent brightness (V mag.) plotted against the redshifl (z) for various groups of quasars believed to be physically associated. From Arf>, Liege Conference.
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in Chapter 4, we would expect 12 to 15 more tion involving bright apparent magnitude
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quasars than expected from average back- quasars. This panel cannot be taken too rigor-
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ground to represent the quasars actually phys- ously because the size of the regions have
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ically associated with this jet galaxy. Possibly been arbitrarily adjusted. But the Sculptor re-
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some of the brighter and certainly some of the gion will be considered in much more detail
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fainter quasars represent projected foreground later and the association of the quasars with
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and background objects. In that case, we find the nearby Sculptor group galaxies justified in
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just about a dozen or so quasars which outline detail.
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the expected relation fairly well.
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The final panel in the lower left of Figure
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The other association of quasars discussed 5-4 shows that in the South Galactic Hemi-
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in Chapter 4 was with the galaxy NGC 520. sphere (SGH radio quasars) the quasars might
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Those quasars are shown in the upper-right- be fitted by the brightest (nearest to us) roof-
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hand panel of Figure 5-4. They also appear to relation of all. The direction of these quasars
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outline a roof relation quite well, particularly defines essentially the direction of the Local
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the brighter envelope of points. The actual Group of galaxies, the nearest galaxies to us.
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line has not been drawn in the NGC 520 panel because that would commit us to a zero point for the system, i.e., it would say that we actually believe a certain relative distance for the system. Later, we will encounter confirmatory evidence for NGC 520 being a member of the Local Group of galaxies despite the rather large redshift of the central, disturbed galaxy (z = 2200 km s~'). (We are actually using quasars here as distance indicators for peculiar galaxies!)
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The establishment and verification of this luminosity-redshift relation for quasars forces us to consider the surprising conclusion that the highest redshift quasars (z ~ 2), instead of being the most luminous objects in the universe as has been heretofore supposed, are actually the least intrinsically luminous quasars. This is a startling development but it enables us to pose the most crucial question of all. It is:
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"If the quasars with redshifts near z = 2
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Quasars from three of the densest groups have the intrinsically lowest luminosities,
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on the sky as discussed earlier and illustrated then those that have the brightest apparent
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in Figures 5-1 and 5-2 are now plotted in the magnitudes are the closest quasars to us in
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bottom right panel of Figure 5-4. It is evident space. Where are they located on the sky?"
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that they concentrate around redshift z = 1 as
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if they were more distant objects that had just C. Quasars in the poked above the limiting threshold of discov-
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ery at V = 19th to 20th magnitude.
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Local Group of Galaxies
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Next we come to an area in the sky near
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the constellation of Sculptor. Later in this
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The answer to the question of where the
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chapter, we discuss the evidence for a large lowest-luminosity quasars are located in the
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physical association of quasars in this area. In sky breaks open the box of contradictory in-
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the lower middle panel of Figure 5-4 we plot ferences into which the establishment has so
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the many high-redshift quasars in this group far succeeded in locking this issue. Figure 5-5.
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found by objective-prism techniques (filled shows the plot of all apparently bright radio
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circles). In order to get an idea where the quasars, found from radio surveys over the sky,
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brighter quasars in this area fall we also plot with redshift near z — 2. It is immediately ob-
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radio quasars (open circles). The quasars in vious that there are three to four times as
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this region could therefore satisfy a roof rela- many of these high-z quasars on the half of
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tion moved rather close to us—that is, a rela- the sky toward the Local Group of galaxies
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Distribution of Quasars in Space 69
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than there are in the side of the sky toward the more distant, Virgo supercluster. There really is no way around this result. It requires that many of the known quasars come from galaxies that are among the closest to us. Moreover, this one group of quasars and nearby galaxies spreads over areas of the order of one-third of the visible sky. In some sense, we are imbedded in the edge of the Local Group and would expect to see some of it, at least thinly, in all directions. Since quasars with smaller redshifts are generally intrinsically more luminous and can be seen in more distant, apparently smaller groups in different directions on the sky, and since all this depends on the apparent magnitude level we are looking at, it is not surprising that conventional, nondiscriminating analyses can make, and have made, almost any statement they please about quasar distribution on the sky. In contrast, the lesson we have learned so far in this section is that the intrinsic luminosity of a quasar depends on its redshift, and that at any given redshift, its apparent magnitude depends on its distance.
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This is strong stuff. Even though I feel it follows ineluctably from the observational evidence, it is still necessary, in the old-time scientific spirit, to test it against all the evidence we can get our hands on. The first test we make is to look more closely at that concentration of quasars in the direction of the center of the Local Group. Figure 5-6 shows a region of the sky more directly centered on the Local Group. There we see an obvious line of quasars extending from mid-upper left to lower right. The line originates from the Local Group companion galaxy, M33! We saw in Chapter 2 that, statistically, quasars tend to be associated with companion galaxies, ostensibly because companion galaxies are a younger and more active variety of galaxies. M33 is the famous spiral in Triangulum with spiral arms composed of young, blue stars and glowing hydrogen gas. It is the most conspicious
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companion to the dominant galaxy in our own Local Group.
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M33 is the nearest spiral galaxy of this type to us. Now, we see the nearest quasars to us emerging on a line from this object. I really do not know which is the more exciting, seeing this much maligned idea of local quasars exonerated so dramatically, or the shock of confronting this new and greater mystery of what the quasars are and how they originate from M33.
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There is, of course, the naturally following question of what else is associated with M33. A similar graphical analysis to that of Figure 5-5 and 5-6 shows that there is also a concentration of low-redshift (0.27 < z < 0.47) quasars near M33. But they are all brighter, about 2 magnitudes brighter, than the high-redshift quasars that we have just seen associated with M33. Now we check against the "roof relation derived from Figure 5-4 and see that the luminosities of these lower-redshift quasars are required to be just about 2 magnitudes brighter! (See Fig. 5-8.) So the quasars found associated with M33 confirm this relation.
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Not only do we see quasars of low redshift in this region southeast of M33, but we also see certain radio galaxies of the same redshift. Since many of the low-redshift quasars have fuzzy edges when closely inspected on good photographs, these radio galaxies, which have somewhat fuzzier edges, are physically similar and form a continuous class. (The naive insistence of the cosmological group that any spot in the sky that is fuzzy has to be at its redshift distance will be discussed in forthcoming chapters.) But as Figure 5-7 shows, the exciting fact about the distribution of low-redshift quasars and radio galaxies is that not only do they also form an elongated group southwest of M33, but also that the direction of that elongation is rotated slightly counterclockwise from the line of high-redshift
|
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quasars
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70 Distribution of Quasars in Space
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30
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15 Dec
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0-
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2.38 o
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o
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O229
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236 % 203 O207
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no o° Q180
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R.A.
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196' c
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/ 12
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2.35 -
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o
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Figure 5-5. A plot o/higfi-reds/u/t
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quasars all around the sky.
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Redshifts are written next to the
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position of each quasar. The center
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i
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of the Local Group of galaxies is at
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10
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rougWy R.A. = 0h 40m, Dec.
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= +41°
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What this must mean is that the quasars are indeed ejected from galaxies, as we saw in Chapters 3 and 4, but that ejection direction does not stay fixed in space. As a function of time we would expect it to rotate because the ejecting galaxies rotate. Quasars ejected in one direction should also be older than quasars ejected in a later direction. This implies that what are now the lower-redshift quasars
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were ejected earlier and that as time progressed they became more luminous and evolved from high redshift to their present low redshift. That is, the quasars became more like peculiar, high-redshift, companion galaxies. This represents the most provocative direction in which to follow up these results, as will be discussed later. But at this point I would like to cement absolutely the
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QUASARS 0.3^ S,, «7.0 U0<z<2.70
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45°
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23
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21 20
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Figure 5-6. High-reds/uft quasars of given radio strength in the vicinity of the center of the Local Group. The Local Group companion galaxy, M33,
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is shown by an open square. From Arp, Journal of Astrophysics and Astronomy (1984).
|
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|
Distribution of Quasars in Space
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71
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|
7 VS16.8; PKSAC Rad. Oal.*.27<:z< A8 all V;
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>«.
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o°°,
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Figure 5-7. The distribution
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- toward M33 of high-redshift quasars (open circles), bright,
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low-redshift quasars (filled
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circles) and low-redshift radio
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20 galaxies (crosses).
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unique nature of the distribution of the quasars around M33 and their association with M33.
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First of all, there is the point about the reality of the concentration and alignment of quasars southeast of M33. Accepting its reality, as we shall see in a moment, leads to disaster for the conventional viewpoint. Given this end result, the usual procedure for the establishment, as in the precedent of previous events, would be to perform a statistical analysis on the distribution in which boundary assumptions would be adjusted until they yielded a nonsignificant result. Fortunately, this has been forestalled by a sophisticated and thorough statistical analysis performed by the astrophysicists J. Narlikar and K. Subramanian at the Tata Institute in Bombay, India. They show that the quasars in Figures 5-5 are significant concentrations, with probabilities only about 10"4 of being random distributions, and that the quasars are also significantly aligned by the same large factors of significance. This is an important piece of mathematical analysis, but for myself, and I suspect for many readers, simply the visual evidence in Figures 5-5 and 5-6 demonstrate quite forcefully that there is a real alignment of quasars emerging to the southwest from M33.
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In order to see exactly what this quasar alignment consists of, we outline the greatest concentration of high-redshift quasars in the vicinity of M33. We then display all the radio quasars present inside this region in the apparent magnitude-redshift diagram in the top panel of Figure 5-8. We use radio quasars throughout because they are drawn from radio surveys, which are generally homogeneous all over the sky at any given declination. In the bottom diagram we display all the radio quasars in a much larger comparison area in the opposite direction in the sky (the Virgo supercluster region). We see that the distributions are completely different. The most important difference is the large clump of high-redshift quasars which are relatively bright in apparent magnitude (around V ~ 18 mag.) which are present southwest of M33 but are essentially absent in the opposite quadrant of the sky. These high-redshift quasars are simply the closest large group of quasars to us, associated with the Local Group galaxy M33.
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Given the reality and uniqueness of the quasar alignment with M33, the last remaining escape for the cosmological adherents is to claim, "selection effects." The disproof of this possibility is very cutting. The reason is
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72 Distribution of Quasars in Space
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15 16 V mag. 17 18 19
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M33 SW
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Figure 5-8. Inside the area southwest of M33 are shown all radio quasars in an apparent magnitude^edshift diagram. Below is shown a larger comparison are in the opposite direction of the sky.
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that all the quasars we are dealing with are undeniably real quasars—spectra which identify the redshifts exist for all of them. Therefore the only possible way to make the concentration southwest of M33 disappear is to discover many more high-redshift radio quasars in other directions all over the sky.
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But, it is preposterous to suppose that only radio quasars of high redshift were selectively not observed in other regions of the sky.
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Yet this is what the conventional interpretation must claim in order to save the situation. It should be made very clear that they have the responsibility of producing, and publishing, the spectra of these missing quasars near z— 2, either that or admit their distribu-
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tion is anomalous. If they admit the latter they will have a grotesque inhomogenity on the largest scale of the universe pointing at the observer (because the inhomogenity contains a range of redshifts around z — 2). They would also have to ascribe the alignment with M33 as an accident.
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Two further interesting comments can be made about Figure 5-8: One is that the quasars in the top panel are all very bright in apparent magnitude. That is as required by their belonging to a galaxy as close to us in space as M33. In fact, the "roof relation derived from the analysis earlier in this chapter is confirmed in Figure 5-8 by the fact that the quasars of redshift z ~ 1 or less average about two
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Distribution of Quasars in Space
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73
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magnitudes intrinsically brighter than quasars around z = 2. The other interesting feature of the quasars southwest of M33 is that very few quasars of faint apparent magnitude appear in this area. It is as if we were seeing a cloud at the distance of the Local Group of galaxies and then a relative void beyond.
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The "cloud" distribution is a necessity on both the cosmological and local interpretation of quasars. That is because Olbers' paradox would demand an infinite sky brightness if they' were not in clouds. (Olbers merely pointed out that a uniform distribution of luminous objects extending to an indefinitely large radius in space would necessarily lead to an indefinitely bright sky instead of the dark night sky we observe.) In the cosmological interpretation, the catastrophe is avoided by invoking "evolution" of quasars. That is, beyond a certain distance, the conventional viewpoint resorts to simply turning out the quasars (saying they are too young to have formed). So, they are dealing with a limited cloud, but one of very large dimensions. The local- interpretation, we see, simply has smaller dimensions to its clouds of quasars. Since these local quasars are generally less luminous than the galaxies they are grouped with, they avoid an infinite sky-brightness in the same natural way as do the groups and clusters of galaxies to which they belong.
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But there is an added fillip to this necessary cloud picture:
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Fred Hoyle pointed out an absolute mathematical disproof of the cosmological nature of quasars. Mathematically he showed that in order to reproduce, on the cosmological assumption, the observed numbers of quasars as a function of redshift, their luminosity function must be very steep. (That is, at a given distance, or redshift, the number of quasars must increase rapidly as their luminosity decreases.) All the conventional analyses indeed require this very steep luminosity function. Yet as Hoyle points out, the observations strongly violate this requirement. You
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can see a dramatic example of this in the top of Figure 5-8. Between redshifts 0.2 :£ z S 1.0 there are a number of quasars between apparent magnitude 16 ^ V S 17 mag. If the conventional luminosity function were really valid, then we should observe ten times as many quasars in the redshift interval between 18.5 :£ V ^ 19.5 mag. Actually, we observe practically none. There could scarcely be a more clear-cut observational contradiction of the cosmological requirement. It may or may not be hard to believe, but many astronomical research centers do not even have the Hoyle publication. One center where I brought it to their attention made the reply that: "Well, the mathematics are correct but the observations are not good enough to test the claim."
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It would be a marvelous confirmation of what we have learned about quasars in the Local Group if we could look at the next most distant group of galaxies and observe something like the same phenomena at a correspondingly smaller scale and fainter apparent magnitude. That opportunity is presented to us by a group of galaxies located in the constellation of Sculptor.
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D. The Sculptor Group of Galaxies
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A group of galaxies in the southern hemisphere of the sky lies roughly 2-3 times farther from us than the Local Group galaxies such as M33 which we have just discussed. Two dominant galaxies define the Sculptor Group. One is the impressive spiral galaxy NGC 300, which is of much the same type as M33 yet still close enough to see distance-indicating Cepheid variable stars in the arms. The other, NGC 55, has comparable size but more irregular shape. Now an extraordinary stroke of good luck occurred when two astronomers at the U.S. National Observatory in Chile, decided to observe a sample of quasars. They picked a declination zone that ran high overhead for them (Dec = -40°) and observed a
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74 Distribution of Quasars in Space
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STRONG LINE WEAK LINE
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TOTAL- 116
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STRONC LINE QUASARS TOTAL • ««
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Figure 5-9. The numbers of
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WEAK LINE OUASARS TOTAL* 32
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objective prism quasars in the Dec = -40° zone. Note that the
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proportion of strong-line quasars
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rises just at the position of the
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Sculptor group galaxies NGC
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RIGHT ASCENSION (HRS)
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300 and NGC 55.
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long, narrow strip of sky, 5 degrees wide, run- But I noticed that the quasars at the ends of
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ning from west to east. The good luck was the strip contained proportionally more
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that this strip runs right across our Sculptor "weak-lined" quasars. That is, the emission
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galaxies NGC 300 and NGC 55. The begin- lines identifying them as quasars were fainter
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ning and the end of the strip lies outside the and they were consequently more difficult to
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Sculptor group and can be used to compare to discover. If the photographic emulsions were
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the results in the center of the strip.
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really less sensitive at the ends of the strip,
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An uncomfortable result became appar- then a proportionally smaller number of these
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ent as soon as they plotted their results. A quasars should have been found rather than a
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good many more quasars were found in the larger number. When I tried to publish this
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center of the strip than at the edges. Since result in the British journal, Monthly Notices
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these two astronomers accepted unquestion- of the Royal Astronomical Society, it was sent to
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ingly that the quasars were out at the far one of the original two authors to referee.
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reaches of the universe, this result obviously Needless to say, it was not published. It was
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could not be correct. Therefore, after the fact, almost stopped again when I sent a short ar-
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they decided that the photographic emulsions ticle to Nature, but, thanks to the last-minute
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they had used were less sensitive on either intervention of an editor, it finally appeared.
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end of the strip than they were in the middle The diagram shown in Figure 5-9 is from that
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of the strip!
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article and shows how the concentration of
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This was duly published and accepted strong-line quasars rises dramatically at just
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Distribution of Quasars in Space 75
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-32°DEC -36°-
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-40°-
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-44C
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OBJ.PRISM QUASARS U <Z< 2.7 17.0<V
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c? 8
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of
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Figure 5-10. Plot of the high-redshift quasars in the region of the Sculptor Group galaxies.
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the position of the Sculptor group galaxies, NGC 300 and NGC 55. It is interesting that we have here more than just a concentration of quasars in this region. We have a concentration of a particular kind of quasar. (The Appendix to Chapter 1 references articles which discuss factors of 10 density discrepancies across this region.)
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I was able to measure more quasars north of the Dec = -40° strip, and thus extend the areas of homogenous quasar discovery to the next strip around NGC 300 and NGC 55. These results are shown in Figure 5-10. The quasars in this entire area are now seen to have a very interesting distribution. Of course, there is the general excess of quasars demonstrated by Figure 5-9. But in addition these excess quasars tend to group around the major galaxies, NGC 300 and NGC 55.
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The densest distribution in Figure 5-10 forms a line southeast of NGC 300 about 9 degrees long. In Figure 5-7 we saw a similar elongated alignment of quasars emerging from M33. Of course, the line from M33 was about 5 times longer in angular extent, but M33 is less than half as distant. These lines also must have arbitrary projection angles in space. Finally we can check the apparent magnitudes of the quasars in these lines, and
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as Figure 5-11 shows, the NGC 300 quasars are just about 1.5 magnitudes (a factor of two in distance) fainter. Therefore we see that in both the closest and next closest groups of galaxies to us in space we identify elongated distributions of quasars emerging from the major spiral galaxies in each group. Moreover, the scale of the distribution on the sky and apparent magnitude of the quasars supports the known fact that the second group of galaxies is just about twice as distant. Of course, lines of quasars are exactly what we observed in the ejecting galaxies NGC 1097, NGC 520, and M82 in the preceding chapter. •
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E. The Quasars Belonging to M82
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It is more than interesting now to re-examine the third most distant group of galaxies from us. That is the M81 group at about 1 magnitude greater distance modulus than NGC 300. The major active companion in that group, M82, was found to have an "ejection cone" of three quasars with redshifts around z ~ 2 emerging from it (Chapter 4). This is the beginning of a line, or elongated distribution.
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These quasars are very faint, between 20th and 21st magnitude, as shown in Figure
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76 Distribution of Quasars in Space
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QUASAR APPARENT MAGNITUDE
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5-11. So we apparently have a glimpse, at apparent magnitudes just above the plate limit, of a similar line of high-redshift quasars emerging from an active galaxy in also the third most distant group of galaxies. Figure 5-11 demonstrates that the apparent brightness of their associated quasars scales accurately as would be required of galaxies at these three different distances.
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Summary
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What we have done in this chapter is to account for large numbers of quasars. Referring to the numerous quasars mentioned in the beginning of the chapter that were not obviously associated with any galaxy, it turns out now that many are, in fact, associated with galaxies—it is just that the galaxies are so close that the associations stretch over large areas of the sky. It also turns out that the high-redshift quasars around z « 2 are not generally seen beyond the relatively nearby M81 group. That means that we have highredshift quasars which belong to M33, and possibly to other members of the Local Group, projected over large areas of the sky, probably quasars that belong to our own galaxy which could be projected in almost any direction in the sky, plus various quasars that are contributed by more distant galaxies and groups like Sculptor and M81.
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It will require some study and discrimina-
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Figure 5-11. Comparison of op/wrent magnitudes of high redshift quasars in M33, NGC 300, and M82 lines. See Arp (1984, Fig. 4) for details. Note that the high redshift quasars associated with the most distant of the three galaxies, M82, are almost at the discovery limit.
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tion to sort out which quasars belong to which groups; possibly, in a number of cases, we can never be completely certain. The picture is further complicated when we consider quasars with redshifts around z = 1. These are intrinsically brighter and can be seen at greater distances. Therefore they contribute some very bright apparent magnitude quasars which belong to extended nearby groups and in addition contribute fainter, smaller-scale groupings. But the smaller-scale groupings appear in regions of the sky which do not have much relation to the nearby, larger groupings.
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What is clearly needed now are careful, homogeneous quasar searches with various techniques to uniform limiting magnitudes all over the sky. Then detailed interpretation can be made. This is the necessary, hard scientific work that should have been undertaken long ago. It is simply irresponsible to say, "I know all the important things about the universe—I do not have to study it. I need only to take a sample here and a sample there and announce that my model is now correct to several decimal places." This approach reminds us of the blind men feeling the elephant. One feels the leg and says an elephant is a tree, another feels the trunk and says it is a snake. In current extragalactic astronomy, one group has gone a step further by trying to eliminate all the others and to be left proudly waving the tail and proclaiming, "There is no uncertainty about the answer now."
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Distribution of Quasars in Space
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77
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Before we go on to the next chapter, however, we have to face a difficult and challenging problem. The problem is, namely, that associating the quasars with nearby galaxies means that their redshifts cannot be due to the Doppler effect of a recession velocity at great distances in the universe. Some other explanation for the high redshifts of the quasars must exist. What this explanation is, is a matter of spirited debate, as it should be, among that small band of astronomers who believe in the noncosmological redshifts of quasars. We will come to this animated discussion in a few chapters, but before that I would like to talk about nonvelocity redshifts in galaxies. That's right, galaxies. The reason for this is that quasars are small, mysterious objects that invite speculative theories. Perhaps they are redshifted by a strong gravitational field, perhaps by high ejection velocities, perhaps by robbing the photons of
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Appendix to Chapter 5
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their energy by some scattering process. Some theorists have been intrigued with the idea that quasars are distant objects which are gravitationally lensed, and amplified in brightness, by galaxies near their light path. But evidence points to the fact that galaxies can also have nonvelocity redshifts. If this is true it presents us with objects we know vastly more about. We can actually study rotation, dynamics, and chemical composition of the constitutent stars in many galaxies. How could an entire galaxy have a nonvelocity redshift? The answer to this may be even more far-reaching and staggering than the answer to the same question about quasars. And, if the more energetic, compact forms of galaxies can be shown to be physically continuous with quasars then the answer to the redshift riddle for quasars may be the same for quasars as for galaxies.
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PAIRS OF QUASARS The tendency of quasars to pair has been obvious for a long time. In 1970(Astron. Joum. Vol. 75, p. 1), I pointed out
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a number of quasars which fell conspicuously closer to each other on the sky than average and had a number of properties such as apparent magnitude, radio properties, and redshifts which resembled each other more than one would expect for randomly occurring objects. Of course, the redshifts were, typically, enough different so that they would invalidate the cosmological redshift assumption if the quasars were actually physically associated. I remember, in the early days, Fred Hoyle discussing the obvious similarities between 3C286 and 3C287, two quasars close together in the sky. Today, it is impressive to run your eye down modem lists of quasars and see how many obvious pairs stand out.
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This phenomenon was quantitatively investigated by G. R. Burbidge, E. M. Burbidge, and S. L. O'Dell in 1974. They demonstrated, using only the few very close quasar pairs known at the time, that the redshift differences could not be reconciled with redshifts indicative of distance. Poof! There went the cosmological hypothesis! Well, one would have thought so, but it was privately stated with calm assurance that this calculation did not count because the test was made after the quasars had been discovered. This is the old "a posteriori" argument which was now further deformed to say, "You cannot test any data that already exists." Undaunted? Well, I cannot say, but Burbidge and Narlikar nevertheless recently went on to make the calculation using all the quasars discovered after the time of their first analysis. They now obtain a probability ~ 1O\ less than one chance in ten thousand that these pairs can be accidental (see references following).
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An illustration of how things work in this game was accidentally revealed to me shortly before this last Burbidge and Narlikar paper. An astronomer analyzing this quasar data found a disturbingly significant excess of these same pairs. He said, "Well, this is obviously a selection effect caused by astronomers looking in the vicinity of radio quasars for nonradio quasars." (Of course, these cases are minuscule in number and could be easily identified.) But as he "normalized out" this effect and sent his paper proclaiming another proof of the cosmological nature of quasars off for instant publication, he smiled at me and said, "Gee, Chip, I really would love to find some hard evidence for noncosmological quasars."
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The latest paper on this subject (European Southern Observatory Preprint No. 422) purports to refute the physical pairing of quasars of different redshift:. But the analysis mixes physical groupings of widely different distances and hence widely different characteristic separations. Even so, close inspection of the graphical results shows consistently more close separations than expected. The effect would be even more conspicuous if the fitted line had been drawn accurately through the points representing large separation.
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78 Distribution of Quasars in Space
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Redshift Periodicities in Different Groups of Quasars Now that we have established the existence of different physical groups of quasars, we can take another, more illu-
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minating look at the preferred values of quasar redshifts that are discussed toward the end of the first chapter. We saw there that the three quasars in NGC 1073 fit almost exactly the mean periodicity of all quasars taken as a whole. But other physical groups of quasars can have slightly different periodicites. Because the spacing between periods follows the rule that the intervals in the logarithm of (1 + z) are constant A (tog 1 + z) = const.), a group with a slightly different constant will have intervals which become progressively1 larger as larger redshifts are considered. An example of this is shown in Figure 5-12.
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i } OBJECTIVE PRISM NGC 3842 NGC 1073 } ALL QUASARS
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Figure 5-12. The preferred periods for all quasars as a whole are shown along the bottom of the strip. Preferred periods for the objective prism quasars (which are dominated by the Sculptor group quasars) are shown along the top. The points indicate how well the triplets of quasars discussed in Chapter 1 fit these preferred periods.
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The quasars selected by objective prism searches (Box and Roeder, see Appendix to Chapter 1) are dominated by the large group of quasars associated with the Sculptor group of galaxies discussed earlier in this chapter. We see that the periodicity of this objective-prism selected group of quasars has a slightly larger constant in the logarithm. Another physical group, the three quasars around NGC 3842 shown in the first chapter, fit this larger spacing. In general, each group of quasars we have identified as physically belonging together tends to have either a slightly smaller or slightly larger spacing than the mean of all quasars. This confirms the periodicity, but gives a broadness to the values of preferred redshift for all groups lumped together. Each individual group, however, tends to have more exactly defined peaks of preferred redshift. The final chapter in this book makes some suggestions as to what might cause the fundamental periodicity. What causes the slight difference from group to group? There is only a hint, which will be discussed later in Chapter 9 when we examine Virgo cluster quasars. It is clear that further study and analysis of these periodicities could furnish invaluable insight into these most basic physical properties of matter.
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References to Papers Covering Material in Text
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1981, Oort, J. H., Arp, H., and de Ruiter, H., Astron. and Astrophys., 95, p. 7. This paper investigates the properties that quasars would have if they were at cosmological distances and members
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of superclusters. I thought I might initiate a healthy precedent in the field by looking at the data from a standpoint different from my own personal belief. The paper demonstrates the masterful astronomical knowledge of Prof. Oort and it was a privilege to write the paper with him, but I must admit that the results which I felt to be important about the separations of high-z quasar pairs being too large to be accommodated by the cosmological model were not included in the paper. 1983, Arp, H., "Groups, Concentrations, and Associations of Quasars' in "Quasars and Gravitational Lenses," 24th Liege Astrophysical Colloquium, Institut d'Astrophysique, June 1983.
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This review paper developed the data on luminosities of quasars in groups at different distances. The discovery of the line of quasars from M33 first emerged in this presentation. The conference is also interesting to read for the number of papers critical of my general viewpoint about quasars.
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Distribution of Quasars in Space 79
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1983, Hoyle, E, "A Gravitational Model for QSO's," Preprint Series No. 88> Department of Applied Mathematics and Astronomy, University College, P.O. Box 78, Cardiff, England.
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This refreshingly candid discussion of the quasar problem argues for a gravitational mechanism as a cause of the redshift. I do not personally subscribe to this explanation, but the discussion of quasar phenomena is rigorous and informed and the science is top-notch. This monograph is in very few libraries and must be obtained from the University of Cardiff. 1984, Arp, H., "The Nearest Quasars," Publ. Astron. Society of the Pacific, 96, p. 148.
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This paper investigates the line of quasars southwestof M33 and shows how low-redshift quasars and radio galaxies are rotated slightly from the line of high-redshift quasars. Of great importance in this paper is the discussion, the most fundamental I could make, of the arguments previously advanced to prove that radio galaxies had to be at their redshift distances. 1984, Arp, H., "A Large Quasar Inhomogeneity on the Sky," Astrophys. Joum. (Letters), 277, p. L27.
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This paper offers additional evidence that the quasars southwest of M33 cannot be an accidental fluctuation in a uniform distribution and that this observed distribution makes no sense on the cosmological model. A sad by-note is that George Abell, who was a classmate of mine in my graduate-school days, was refereeing this paper. One of the last letters he wrote before his untimely death said that he could not explain how it occurred, but he was sure the alignment was some sort of selection effect. 1984, Arp, H., "Distribution of Quasars on the Sky," Journ. of Astrophys. and Astronomy, 5, p. 31.
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This was an invited paper by V. Radakrishnan for the Jubilee Issue of the Journal of Astrophysics and Astronomy. It developed further the picture of the Local Group, quasars with z~2 and established consistency between the line of quasars in the Local Group and the next nearest Sculptor group. It showed that inhomogeneities of distribution of the quasars were reflected in inhomogeneous distribution of radio sources. The radio sources have, in the past, been supposed to be uniformly distributed and it is very important to now reinvestigate this important question. 1985, Narlikar. J. V. and Subramanian, "A Statistical Significance of a Large Quasar Inhomogeneity in the Sky," Astron. Astrophys., 151. p. 264.
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This shows the concentration of quasars southwest of M33 to be highly significant. 1985, Burbidge, G. R.. Narlikar. J. P., and Hewitt, A., Nature, 317, p. 413.
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This paper gives the most recent calculation of the chance of accidentally observing the known number of apparent quasar pairs with discordant redshifts. The probability is now less than one in ten thousand, so that the cosmological hypothesis is dropping back badly from an already very bad, earlier position. See the text here and Nature, 323, p. 185 for the most recent exchange of viewpoints.
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80 Distribution of Quasars in Space
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GALAXIES WITH 6 EXCESS REDSHIFT
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In the normal course of observing the sky with telescopes, we expect to see galaxies near to each other in groups. When we measure the displacement of the absorption and emission lines in their spectra, we expect to find the redshifts of these galaxies to be very close, differing by only a few hundred kilometers per second (km s"1)-
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When we do see a much larger redshift, we instinctively feel that it is an unrelated object at a much greater distance in the far background where the expansion velocity of the universe is carrying it away from us more rapidly. It is an enormous shock therefore when we measure two galaxies that are interacting, or connected together, and find that they have vastly different redshifts.
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That is what happened when I measured the redshifts of the two galaxies pictured in Figure 6-1. It was 1970 and Palomar observers still had to ride all night in the cage of the 200-inch telescope in order to obtain direct photographs and spectra of astronomical objects. An observer was usually lucky to get two spectra in a night of objects as faint as the ones in Figure 6-1. But I was following up interesting objects from my Atlas of Peculiar
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Galaxies, and I was interested in that class of objects where companion galaxies were found on the end of spiral arms. As in the case of the quasars, this study led to big trouble when I discovered the redshifts of the two connected objects differed by Az = 8,300 km s'1.
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The trouble lies in the fact that one cannot even postulate that by some freak accident two galaxies are in the same region of space and that the smaller galaxy is running past the larger galaxy with a relative velocity of 8,300 km s"'. At that rate of passage the companion would be unable to pull out a filament from the larger galaxy. The gravitational pull needed to shear stars out of their normal orbits cannot build up in the relatively short time that such a rapid encounter would allow. We therefore conclude that the objects cannot have this velocity difference and we are back to an object with an intrinsic redshift. Only this time, it is not just a compact object like a quasar, but a whole galaxy of stars, each star of which must share, for some mysterious reason, a redshift much elevated above the normal.
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Of course, the first thing one considers in a case like this is whether this could possibly
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Galaxies with Excess Redshifts 81
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Figure 6-1. The large, disturbed Seyfert galaxy, NGC 7603, with a companion galaxy apparently attached by a filament. The redshifi of the larger galaxy is 8,700 km s-' and of the smaller is 17,000 km s'. These pictures were when by Roger Lynds with the Kitt Peak National Observatory 4-meter telescope in 197i and have recently become available through the information adding of separate pictures by Nigel Sharp.
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represent a background object that just accidentally happens to appear projected onto the end of a luminous filament belonging to a more nearby galaxy. So back I went into the cage on my next observing run in order to obtain the longest, deepest and best possible photograph of the object. It showed the connection strongly, as did all other pictures like the one shown in Figure 6-1.
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Unlike the connection between NGC 4319 and Markarian 205 discussed in Chapter 3, nobody ever tried to question the reality of the luminous arm emerging from NGC 7603. What little debate took place in this case
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hinged on whether its connection to the companion was real or only apparent.
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A number of arguments attested to a real connection. First of all, the larger galaxy, NGC 7603, is a Seyfert galaxy, a fairly rare kind of galaxy with an active nucleus. Secondly, NGC 7603 is all torn up inside and nothing else is around except the companion to account for this disruption. Thirdly, only one luminous arm or filament emerges from NGC 7603 in such a way as to make it an almost unique object among galaxies. This unusual arm ends right on the companion!
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All this, naturally, is extremely unlikely to
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82 Galaxies with Excess Redshifts
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be an accidental occurrence. But still I was not satisfied and I studied the companion closely. The original plate showed that the form of the companion, with its broad, bright nucleus and a discretely lower surface brightness disk, is unusual. But the bright rim on the outer edge of the companion, just where the arm from NGC 7603 connects, proved to me that there is actual physical interaction between the two. *
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But the spectrum of the companion puzzled me. It had only the usual absorption lines found in ordinary galaxies of older stellar population type. As we will see, a number of other examples of these anomalously redshifted companion galaxies tend instead to show emission lines and absorption lines that are more characteristic of a younger stellar population. The evidence from the nature of the connection and the peculiarities of the galaxies establish rather conclusively that the present two are connected, but the spectrum of the companion so far offers no clues as to unusual physical conditions that might account for its 8,300 km s"' higher redshift.
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This was the only example of a strikingly discordant redshift that turned up this small class of connected companions in the Atlas of Peculiar Galaxies. But the much larger Catalogue of Southern Peculiar Galaxies and Associations, initiated a few years later by Arp and Madore, furnished more examples of smaller companions connected to, or interacting with, larger galaxies. These were the productive days when I used the 2.5-meter Carnegie Institution telescope in Chile to get further photographs and measure spectra of these objects. In the first batch of seven candidates, I found three to have highly discrepant redshift values. Later more turned up. A sampling of these objects is shown in Figures 6-2 and 6-3 here. The luxury of having long runs on the telescope allowed the spectra of these objects
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to be studied in some detail. There are many extraordinary peculiarities discovered in these spectra which should be followed up. But as a preliminary classification I have noted in the sample of them that are listed in Table 6-1 whether the spectra have emission lines and whether the absorption lines are characteristic of a young or old stellar population.
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We should understand that if we just go around picking galaxies at random in the sky and studying their spectra that by far the most common spectrum we will find is nonemission with late-type stellar absorption. Table 6 shows, however, that the discordant redshift companions characteristically exhibit excited, emission lines and young stellar population absorption lines. If they were just accidental projections of ordinary background galaxies they would have the characteristic spectra of background galaxies. This is a clinching proof that these excess redshift companions are really physically associated with the lower redshift galaxies.
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The way in which I would think a rational astronomer would have to handle this disturbing situation is to look carefully at objects like NGC 7603 in Figure 6-1, or at some of the examples in Figures 6-2, 6-3, and 6-4, and say: "Well, these are certainly connected objects, the eye readily tells us they could not be anything else." Then, he puts aside the pictures and says, "This goes against everything I have been taught about redshift-distance laws. They must be just accidents." But then he thinks about the confirmatory evidence from their spectra (and the abundant other evidence discussed in this book) that demonstrates they are not accidents. He then goes back to the pictures and says, "Well, it seems that they are not accidents and when I actually look at the pictures I can see many more confirmatory details which demonstrate that this is just simply the surprising, but actual
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•Photographs taken shortly afteward in 1973, with the Kitt Peak National Observator's 4-meter telescope confirmed the peculiar bright rim on the companion, its deformed shape and the brightening of this rim near its point of contact with the arm from NGC 7603- The existence of these confirming pictures not known to me until recently. These latter photographs are shown in Figure 6-1.
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Galaxies with Excess Redshifts 83
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• •* - •
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AM 2054-221
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_:-"„.
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•§swTm
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Figure 6-2. Four examples of interacting high-redshift companions (marked by arrows). See Table 6-1 for data.
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Figure 6-3. A particular!)! interesting example of a high rahhift companion (AM2006-295). Arrow points to condensation in arm with 22,150 fern s 'excess redshift.
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TABLE 6-1 Sample of Connected or Interacting Galaxies with Large Discordant Redshifts*
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Main Galaxy
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Companion
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Type of Spectrum
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Excess Redshift i (km s)
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Illustrated in Figure No.
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NGC 7603 AM0059-402 AM0213-283
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AM0328-222
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AM2006-295
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NGC 1232
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NGC 53
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AM2O54-221
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Comp SE Comp S Comp N
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Comp S
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KNSW GalB
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Comp N
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Comp E
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late absorption late absorption strong emission early absorption emission, early absorption weak emission, peculiar absorption emission, early absorption emission, early absorption emission late absorption
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+8,300 +9,695 + 14,021
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+17,925
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+ 22,350 + 26,210
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+ 32,774 + 36,460
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6-1 Arp. J., 239, 471 6-2
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6-2
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6-3
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6-4 6-2
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6-2
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*As pictured in Figures 6-2, 6-3, and 6-4. Ft r a more complete listing of cases see Astruphysical Journal. 263, p. 70. "Late absorption" described a spectrum typical of low-iuminos ity, older stars, "Early absorption" is a spectrum typical of high-luminosity, younger stars.
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86 Galaxies with Excess Redshifts
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way things are." It is a rare occasion when a person, even a scientist, is able to really look at a picture without forcing it into a frame of prior reference.
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It is, in fact, instructive to look more closely at these pictures. For example, in Figure 6-1 one sees two (stellar appearing?) condensations in the filament leading to the companion. This is even stranger behavior for a part of a galaxy to exhibit. What are they? What would spectra with a large telescope and the newest spectrographs reveal about them? Then there is the three-armed spiral galaxy shown in Figure 6-3. Do you realize how rare three-armed spirals are? And this third arm originates from a point midway out along one of the two symmetrical arms! The discrepant, redshift object occurs in the middle of this third arm. How did it get there?
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These questions call for a working hypothesis within which we can try to organize the disparate facts presented by the observations. But we have already described an ejection hypothesis that was needed to explain the origin of quasars in the earlier chapters of this book.
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There we saw that the compact objects that were to become quasars, the protoquasars, must emerge from the galaxy's nucleus as relatively small, high-redshift objects and later expand, with their redshifts decaying and the objects becoming more like compact, peculiar companion galaxies. There are several advantages to this hypothesis for the discordant companions described here. (I stress that this is only an empirical hypothesis at this stage— a working scheme to connect the various observations which cannot be explained by the current theories about galaxies.) One advantage is that only one explanation would have to be invented to explain the excess redshifts of both quasars and companion galaxies. If there is a continuous physical evolution between the two, as there appears to be a continuous range of physical properties between them, then the same mechanism for nonvelocity redshifts, in differing amounts, could explain both.
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At this point, two comments should be made: (1) The companions with the highest redshifts which are discordant (45,000 km s1 corresponds to a z =0.15) are in the same redshift range as the smaller redshift quasars. (The brightest apparent magnitude quasar in the sky, the famous 3C 273, has z =0.16.) (2) The companions with the highest excess redshifts are spectroscopically the most like quasars. The puzzle I encountered in the spectrum of the companion to NGC 7603 could be resolved if the spectra with relatively small excess redshift are relatively normal, but the spectra become more abnormal as the excess redshift grows. A glance down Table 6-1 shows that with increasing excess redshift, the spectra contain more excited emission lines and younger stellar absorption lines. Quasars, are of course, characterized by high temperatures and conspicuous emission lines, that is, they are the most extreme of these objects. As for the young stellar absorption spctra, extensive observations of the prototype quasar, 3C 48, enabled the astronomers J.B. Oke and T. Boroson to proudly announce that if had the underlying absorption spectrum of a galaxy—but the absorption spectrum is of the young stellar type!
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This last point about underlying galaxies is an interesting and much belabored one. A number of astronomers who have attempted to defend the status quo have tried very hard to prove that underlying all quasars are galaxies. The idea was that there might be some uncertainty about quasars because they are exotic objects, but that galaxies are familiar kinds of objects which must be at their conventional redshift distances. Proving quasars to be galaxies, they felt, was proving quasars to be at their redshift distances Oust in case it needed to be proven, which, of course, they claimed was unnecessary). But what has been apparent from the observations all along— even before many of the present investigators started their work—is that quasars and compact, active galaxies are continuous in phyisical properties. So, by proving again that they
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Galaxies with Excess Redshifts 87
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are related kinds of objects they have proven that the evidence for nonvelocity redshifts in quasars is supported by the evidence for nonvelocity redshifts in galaxies—and vice versa.
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It is a cruel fact of life that whatever the current, official theory is, it must explain all the observed facts. A single well-founded, contradictory observation will suffice to topple the whole edifice. But we have seen that the conventional theory that galaxy redshifts can only be due to Doppler velocity has been violated not just once, but in numerous, independent instances. We will continue to see these violations accumulate.
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Figure 6-4. a) The spiral galaxy NGC 1232 with a companion near the end of one spiral arm (gal A) and a small companion near in inner spiral arm (gal B). b) Insert of photograph in infrared wavelength sliou>ing compact blue companion and disturbed arm nearby.
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As of 1982,38 examples of these discordant redshift companions around 24 main galaxies had been published. We cannot discuss them all here but the references for this data are given in the Appendix. One example is so interesting, however, that I cannot resist devoting a few pages to it.
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A. The Large Spiral Galaxy NGC 1232 and its Two Discordant Redshift Companions
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As Figure 6-4 shows, NGC 1232 is a large, beautiful spiral. The companion galaxy near the end of the spiral arm shows the same resolution of knots and features as the main
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88 Galaxies with Excess Redshifts
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galaxy. It is the usual kind of galaxy that large spirals typically have as physical companions. One can even trace the arm which ends near the companion back to the main spiral where it splits, strangely, into a channel about the width of the companion. I would suggest this might be evidence for the companion to have originated within the main spiral and have traveled outward along this arm. Be that as it may, there was never any hesitancy about accepting this galaxy as a run-of-the-mill companion to a large spiral galaxy. Scarce heed was even paid to the fact that the redshifts of both galaxies were cataloged as essentially equal.
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But then an unpredictable event occurred. The cataloged redshift for the companion was found to be in error. The redshift of the companion was really 4,776 km s"1 greater than the main galaxy. One of the foremost galaxy experts of this era, Gerard de Vaucouleurs, who has been rather more open to discrepant evidence than most, nevertheless had the following comment about this development:
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"Until recently I was convinced from appearance and resolution that this was a physical pair, in fact rather similar to our own galaxy and the Large Magellanic Cloud. However, the differential velocity, A V = +4776, forces us to conclude that this must be an optical pair unless you can offer compelling proof that the two are physically connected."
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My own argument was that the companion was not the kind that was found isolated in space, but was of the kind found with larger spirals such as NGC 1232. Nevertheless, I did take very deep photographic plates of the system in order to search for "compelling proof," perhaps in the form of deformations or extensions of the outer regions of NGC 1232 in the region of the companion. I found no further evidence for the association of the companion than was available originally. But I did find something else that
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turned out to be enormously interesting. Tracing back along the same spiral arm
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which ends on the companion I noticed an anomalous thickening and deformation, as if something was perturbing the arm at that point. Next to this disturbed part of the arm, I noticed an object. Purely out of curiosity, and fully expecting an H II (gaseous emission) region at the redshift of the main galaxy, I took its spectrum. There was thereupon one of those rare and thrilling moments in research when you can look down a long corridor into the future. The spectrum showed a redshift of over 28,000 km s"1 (almost onetenth the velocity of light!), far exceeding the mere 1,776 km s"1 of the main galaxy.
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Studying the spectrum was fascinating. There were six separate kinds of peculiarities that indicated the object cannot be any normal kind of background galaxy. Among them the fact of the narrow calcium (K) absorption line implied it was a low luminosity galaxy. But the most compelling argument that the object was at the distance of NGC 1232 was simply that one does not see background galaxies through the disk of a spiral galaxy. The dust and obscuration in the disk of a spiral galaxy, particularly near the arms, simply forms an impenetrable screen. If, by some strange quirk, we were able to see through a thin part of this screen, we would certainly expect a background object to be heavily reddened. But galaxy B, as we call this object, is extremely blue! It is so blue, in fact, that there is no way that it can be any kind of normal galaxy.
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This evidence, even though of the most detailed and quantitative kind, has always been simply ignored. One of the purposes of this book is to bring all this evidence together, to show that it massively contradicts the accepted paradigm, and to challenge the establishment to deal in a responsible scientific manner with the observations.
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In view of our empirical, working hypothesis we can point out that one way an ob-
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Galaxies with Excess Redshifts 89
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ject like B could arrive at a point in a spiral arm, as observed, is to travel along the spiral arm from the nucleus. It is interesting that this is the same arm along which it was speculated that companion A may have emerged. Perhaps even more suggestive is the knot (KNSW) in the three-armed spiral pictured in Figure 6-3. (That was another of those exciting moments where I took the spectrum expecting a low-redshift emission region.) But that third arm, in my opinion, could only have been formed by an ejection phenomenon along the original track of one of the two main arms. The discordant redshift object then lies along the trajectory of that ejection. There is nothing sacred about this hypothesis, but at least it explains why these discordant redshift objects are found in these arms, an explanation which would be rather difficult otherwise.
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The subject of companion galaxies has already been an important topic in this book. We have seen evidence for the origin of highredshift quasars associated with companions in nearby groups of galaxies. Now we have seen evidence for companion galaxies themselves to be peculiar and to have high nonvelocity redshifts with respect to their main galaxy. The subject of companion galaxies will continue to be an important subject in this book because, as we shall see, the structure of the universe we live in is typically that of groups of galaxies here and there, each dominated by one or two large galaxies with the rest of the galaxies forming a group of smaller companion galaxies around them. It is these smaller, compact objects and companion galaxies in groups which again and again furnish the most abnormal and most excessively redshifted objects that we encounter.
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B. The Active Central Galaxy, NGC 4151
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In most groups, the central galaxy is not particularly active at the moment. For example, the central galaxy in our own Local
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Group is M31, a prototypical Sb spiral. (An Sb has a moderate central bulge of stars and not too conspicuous spiral arms.) It contains the majority of mass in the group and is apparently undergoing fairly smooth and regular rotation of its gas, dust, and stars around its center. M81, in the third most distant, major group is an Sb spiral almost identical to M31. Such Sb spirals are typically seen throughout space with their retinue of smaller companions grouped around them. But NGC 4151 is an Sb spiral with a very active nucleus. How active, you may ask! The brilliant point of light in its nucleus is variable, is a source of radio emission and X-rays, and shows broad, high-excitation emission lines. Altogether, the nucleus acts in many ways like a quasar. The person who has studied this nucleus most intensively, and with whom I am well acquainted, has attempted to find clues to the energy sources and energy mechanisms within quasars and active galaxies from largescale programs of observing and analysis of this nucleus.
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But I was always interested in the outer regions of NGC 4151. It is surrounded by a retinue of smaller galaxies. The trouble is that all of these smaller galaxies are of considerably higher redshift. The usual response would be to say that NGC 4151 is accidentally centered on a more distant group of galaxies. Unfortunately for this hypothesis, these smaller galaxies have generally different redshifts between themselves, ruling out their membership in the same group by conventional criteria. As usual, the first step was to get the best possible plate of the field. On a very dark night at Palomar, with exquisite seeing, I obtained the three-hour exposure shown in Figure 6-5. It shows the arm on the north going out and around almost to NGC 4156, the high surface brightness galaxy to the northeast. The other arm of NGC 4151 goes around and out to the south, where it appears to join a smaller galaxy just at the southwest edge of the picture. Since both of these
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90 Galaxies with Excess Redshifts
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Figure 6-5. Deep exposure o/NGC 4151 by Arp until 200-inch Palomar reflector.
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smaller galaxies are of considerably higher redshift than NGC 4151 itself, I made a special effort to follow this up.
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Eventually, I obtained a number of plates and, with Jean Lorre's help, informationadded them to give the high-contrast picture shown in Figure 6-6. I think this picture shows convincingly that a high-redshift galaxy is attached to the end of each NGC 4151 arm. This result seemed so startling that I simply stated it and did not especially emphasize it with respect to the other evidence for the existence of discordant redshifts. But now that further evidence, as discussed earlier in this chapter, shows that objects of excess redshift occur in or along spiral arms, it can be put forward as strong corroborative proof of the phenomenon. It should also be noticed that the values of the redshifts involved are very similar to those in the Stephan's Quintet
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system discussed later, in Section E of this chapter.
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I have to add a note about B. A. Vorontsov-Velyaminov, a Russian astronomer, who in 1957 searched the Palomar Sky Survey paper prints for peculiar galaxies. One of his favorite kinds was companions on the ends of spiral arms. I learned the English word "gemmation" from him—a botanical term meaning budding or outgrowth. He was always searching for a spiral galaxy with companions on the ends of both arms to demonstrate his theory of galaxy formation. I should dedicate Figure 6-6 to him.
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There is a lot more of interest in the NGC 4151 region. It is a very active region in that all sorts of odd objects are found there. The knotty spiral due east of NGC 4151 has H II regions of much larger apparent diameter than those in NGC 4151, even though it is
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Galaxies with Excess Redshifts
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91
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