Astrophysics and Space Science Library 435 Mauro D’Onofrio Roberto Rampazzo Simone Zaggia Editors From the Realm of the Nebulae to Populations of Galaxies Dialogues on a Century of Research From the Realm of the Nebulae to Populations of Galaxies Astrophysics and Space Science Library EDITORIAL BOARD Chairman W. B. BURTON, National Radio Astronomy Observatory, Charlottesville, Virginia, U.S.A. ([email protected]); University of Leiden, The Netherlands ([email protected]) F. BERTOLA, University of Padua, Italy C. J. CESARSKY, Commission for Atomic Energy, Saclay, France P. EHRENFREUND, Leiden University, The Netherlands O. ENGVOLD, University of Oslo, Norway A. HECK, Strasbourg Astronomical Observatory, France E. P. J. VAN DEN HEUVEL, University of Amsterdam, The Netherlands V. M. KASPI, McGill University, Montreal, Canada J. M. E. KUIJPERS, University of Nijmegen, The Netherlands H. VAN DER LAAN, University of Utrecht, The Netherlands P. G. MURDIN, Institute of Astronomy, Cambridge, UK B. V. SO M OV, Astronomical Institute, Moscow State University, Russia R. A. SUNYAEV, Space Research Institute, Moscow, Russia More information about this series at http://www.springer.com/series/5664 Mauro D’Onofrio • Roberto Rampazzo • Simone Zaggia Editors From the Realm of the Nebulae to Populations of Galaxies Dialogues on a Century of Research 123 Editors Mauro D’Onofrio Roberto Rampazzo Department of Physics and Astronomy INAF–Osservatorio Astronomico University of Padova di Padova Italy Padova, Italy Simone Zaggia INAF–Osservatorio Astronomico di Padova Padova, Italy ISSN 0067-0057 ISSN 2214-7985 (electronic) Astrophysics and Space Science Library ISBN 978-3-319-31004-6 ISBN 978-3-319-31006-0 (eBook) DOI 10.1007/978-3-319-31006-0 Library of Congress Control Number: 2016946611 © Springer International Publishing Switzerland 2016 This work is subject to copyright. 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Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. Cover illustration: Image created by Sergio Dalle Ave by combining the HST+Chandra image of NGC 1132 (credit to NASA and STScI) with an image of the ALMA site (credit to ESO) and an image of the 100” Mnt. Wilson telescope (image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California). Printed on acid-free paper This Springer imprint is published by Springer Nature The registered company is Springer International Publishing AG Switzerland To our families with love and gratitude The worth of that is that which it contains, and that is this, and this with thee remains. W. Shakespeare Sonet 74 Foreword Fifty years ago, I was sitting on a couch by a window at my home in Baltimore, Maryland, watching television with my brothers, when, during a commercial break, I turned my head to look out the window and noticed a bright star. Not knowing what star it was, I got up and went out on the back porch to get a better view. I recall for a few moments just standing there, looking in awe up at a sky full of stars. The view was so remarkable that I went back into the house to look for an old constellation book I had, Stars, by Herbert S. Zim, with which I determined the bright star was Sirius. But more importantly, after identifying the star, I read the descriptions of celestial objects given in the book. On one page was a picture of the Andromeda Spiral, the caption of which stated that the galaxy was 750,000 light years away. I could not believe that anything could be so far away. Ironically, Zim’s book was out of date; later estimates put Andromeda at more than 2.5 million light years. I have recounted this story because it shows the draw galaxies can have on people. The minor experience I had, a turn of the head, a bright star, and a picture caption in a book, led me to a life-long interest in galaxies. Galaxies are islands of starlight spread across an almost unfathomable expanse of space and time. When I try and think of a single word that can describe them, I have to say “majestic,” a term I might also use to characterize a beautiful, tall mountain. How can we hope to know much about things so far away? The answer is provided in this book. From the Realm of the Nebulae to Populations of Galaxies: Dialogues on a Century of Research is a detailed compendium of the profound advances in the study of galaxies that have been made since the 1920s when Edwin Hubble discovered Cepheid variable stars in the Andromeda Galaxy. The book is a useful and admirable attempt to bring a century of progress into thoughtful perspective and to present the progress in the field through the outline of a logical chain of events largely involving advances in instrumentation and computing power. Extragalactic astronomy has gone from the domain of a few observers taking long exposure photographs at remote mountain-top observatories to large international collaborations involving space observatories and dozens, if not hundreds, of astronomers. Without a doubt, we are witnessing a golden age of discovery and exploration in extragalactic astronomy. vii viii Foreword Why is the study of galaxies important? Hubble learned the value of such studies when he discovered the Hubble law, which first pointed to the idea of an expanding universe. Extragalactic studies have also led to the discovery of dark matter, stellar populations, and supermassive black holes. Such studies lead us to naturally ask what role our galaxy has played in our existence. Because we are on a planet in orbit around a star that was born in the Milky Way, we can ask how stars form and how the Milky Way provides the raw materials needed for star formation. In order to answer this, we have to know how stars evolve and the role that different kinds of stars and phenomena (like supernovae) play in enriching the interstellar medium with heavy chemical elements. We observe that the Milky Way is a rotating system with a highly flattened shape and can ask not only how it achieved this shape, but also what the mass of the Milky Way is and how that mass is distributed within it. We can observe or infer the kinds of orbits stars follow as they move around the galactic center and can link these orbits to other properties, such as metallicity. Our location in the Milky Way colors our view of the rest of the universe. The study of other galaxies beyond the Milky Way is important because, on one hand, only such studies can provide a perspective on how the Milky Way fits into the grand scheme of galaxies. Multi-wavelength observations, measurement of parameters and scaling relations, recognition of structures, the distribution of galaxies, etc., are essential for understanding how galaxies form and evolve. Then there is the issue of cosmology, observing galaxies over a wide range of distances and lookback times, in order to probe not only the evolution of galaxies, but the evolution of the universe. A glance at the Table of Contents of this book shows that the study of galaxies is basically relevant to all fields of astronomy. The charm of extragalactic astronomy lies not only in its progress over the last century, but in its history before people even knew such things as galaxies existed. Thousands of nebulous objects that were later shown to be galaxies had been catalogued during the 150 years before Hubble made his grand discovery. The mystique of the nebulae stemmed from a lack of knowledge of their distances, but the general suspicion throughout much of the nineteenth century was that most, if not all, nebulae were distant, unresolved star systems. Adding to the mystique was the discovery, in 1845, of spiral structure in some of the brightest catalogued nebulae. The old sketches made with the “Leviathan of Parsonstown,” the home- built 72-in. reflector of William Parsons, the Third Earl of Rosse, are fascinating relics of a bygone era. When we combine these with the beautiful photographs of galaxies presented in, for example, the Hubble Atlas of Galaxies, we come to realize that there is an enormous and complex diversity in the morphology of galaxies. Physically explaining this diversity and the processes that led to it has been one of the major goals of extragalactic research. Trying to summarize the breadth and scope of advances in such a broad field as extragalactic astronomy over a period of a century is a challenge. Rather than only writing a series of reviews themselves to present the stories and advances in galactic and extragalactic astronomy over this time, the authors of this book chose to interview a significant number of the most knowledgeable and dynamic contributors to the field, in order to provide a perspective that only such people could provide.