From The Realm Of The Nebulae To Populations Of Galaxies

In order to outline possible future directions in galaxy research, this book wants to be a short stopover, a moment of self-reflection of the past century of achievements in this area. Since the pioneering years of galaxy research in the early 20th century, the research on galaxies has seen a relentless advance directly connected to the parallel exponential growth of new technologies. Through a series of interviews with distinguished astronomers the editors provide a snapshot of the achievements obtained in understanding galaxies. While many initial questions about their nature have been addressed, many are still open and require new efforts to achieve a solution. The discussions may reveal paradigms worthwhile revisiting. With the help of some of those scientists who have contributed to it, the editors sketch the history of this scientific journey and ask them for inspirations for future directions of galaxy research.

No modern astronomer made a more profound contribution to our understanding of the cosmos than did Edwin Hubble, who first conclusively demonstrated that the universe is expanding. Basing his theory on the observation of the change in distanct galaxies, called red shift, Hubble showed that this is a Doppler effect, or alteration in the wavelength of light, resulting from the rapid motion of celestial objects away from Earth. In 1935, Hubble described his principal observations and conclusions in the Silliman lectures at Yale University. These lectures were published the following year as "The Realm of the Nebulae," which quickly became a classic work.

A thought provoking study of the powerful impact of images in guiding astronomers' understanding of galaxies through time.

The last 50 years have seen a tremendous progress in the research on quasars. From a time when quasars were unforeseen oddities, we have come to a view that considers quasars as active galactic nuclei, with nuclear activity a coming-of-age experienced by most or all galaxies in their evolution. We have passed from a few tens of known quasars of the early 1970s to the 500,000 listed in the catalogue of the Data Release 14 of the Sloan Digital Sky Survey. Not surprisingly, accretion processes on the central black holes in the nuclei of galaxies — the key concept in our understanding of quasars and active nuclei in general — have gained an outstanding status in present-day astrophysics. Accretion produces a rich spectrum of phenomena in all bands of the electromagnetic spectrum. The power output of highly-accreting quasars has impressive effects on their host galaxies. All the improvement in telescope light gathering and in computing power notwithstanding, we still miss a clear connection between observational properties and theory for quasars, as provided, for example, by the H-R diagram for stars. We do not yet have a complete self-consistent view of nuclear activity with predictive power, as we do for main-sequence stellar sources. At the same time quasars offer many “windows open onto the unknown". On small scales, quasar properties depend on phenomena very close to the black hole event horizon. On large scales, quasars may effect evolution of host galaxies and their circum-galactic environments. Quasars’ potential to map the matter density of the Universe and help reconstruct the Universe’s spacetime geometry is still largely unexploited. The times are ripe for a critical assessment of our present knowledge of quasars as accreting black holes and of their evolution across the cosmic time. The foremost aim of this research topic is to review and contextualize the main observational scenarios following an empirical approach, to present and discuss the accretion scenario, and then to analyze how a closer connection between theory and observation can be achieved, identifying those aspects of our understanding that are still on a shaky terrain and are therefore uncertain knowledge. This research topic covers topics ranging from the nearest environment of the black hole, to the environment of the host galaxies of active nuclei, and to the quasars as markers of the large scale structure and of the geometry of spacetime of the Universe. The spatial domains encompass the accretion disk, the emission and absorption regions, circum-nuclear starbursts, the host galaxy and its interaction with other galaxies. Systematic attention is devoted to some key problems that remain outstanding and are clearly not yet solved: the existence of two quasar classes, radio quiet and radio loud, and in general, the systematic contextualization of quasar properties the properties of the central black hole, the dynamics of the accretion flow in the inner parsecs and the origin of the accretion matter, the quasars’ small and large scale environment, the feedback processes produced by the black hole into the host galaxy, quasar evolutionary patterns from seed black holes to the present-day Universe, and the use of quasars as cosmological standard candles. The timing is appropriate as we are now witnessing a growing body of results from major surveys in the optical, UV X, near and far IR, and radio spectral domains. Radio instrumentation has been upgraded to linear detector — a change that resembles the introduction of CCDs for optical astronomy — making it possible to study radio-quiet quasars at radio frequencies. Herschel and ALMA are especially suited to study the circum-nuclear star formation processes. The new generation of 3D magnetohydrodynamical models offers the prospective of a full physical modeling of the whole quasar emitting regions. At the same time, on the forefront of optical astronomy, applications of adaptive optics to long-slit spectroscopy is yielding unprecedented results on high redshift quasars. Other measurement techniques like 2D and photometric reverberation mapping are also yielding an unprecedented amount of data thanks to dedicated experiments and instruments. Thanks to the instrumental advances, ever growing computing power as well as the coming of age of statistical and analysis techniques, the smallest spatial scales are being probed at unprecedented resolution for wide samples of quasars. On large scales, feedback processes are going out of the realm of single-object studies and are entering into the domain of issues involving efficiency and prevalence over a broad range of cosmic epochs. The Research Topic "Quasars at all Cosmic Epochs" collects a large fraction of the contributions presented at a meeting held in Padova, sponsored jointly by the National Institute for Astrophysics, the Padova Astronomical Observatory, the Department of Physics and Astronomy of the University of Padova, and the Instito de Astrofísica de Andalucía (IAA) of the Consejo Superiór de Investigación Cientifica (CSIC). The meeting has been part of the events meant to celebrate the 250th anniversary of the foundation of the Padova Observatory.

As late as 1995, the anticipated widespread population of primeval galaxies remained at large, lurking undetected at unknown redshifts, with undiscovered properties. We present results from our efforts to detect and characterize primeval galaxies by their signature high-redshift Lyman-alpha emission lines utilizing two observational techniques: serendipitous slit spectroscopy and narrowband imaging. By pushing these techniques to their utmost limits, we probe the Lyman-alpha-emitting galaxy population out to redshifts as high as z = 6.5. Galaxies at this epoch reside in a universe which is just 800 million years old, a mere 6% of its current age. As such, this work provides one account of the manner by which observational cosmology has recently shifted from merely marveling at the incredible lookback times implied by the first few high-redshift detections, to the routine assembly of high-redshift datasets designed to address specific astrophysical issues.

Delineating the huge strides taken in cosmology in the past ten years, this much-anticipated second edition of Malcolm Longair's highly appreciated textbook has been extensively and thoroughly updated. It tells the story of modern astrophysical cosmology from the perspective of one of its most important and fundamental problems – how did the galaxies come about? Longair uses this approach to introduce the whole of what may be called "classical cosmology". What’s more, he describes how the study of the origin of galaxies and larger-scale structures in the Universe has provided us with direct information about the physics of the very early Universe.

Delineating the huge strides taken in cosmology in the past ten years, this much-anticipated second edition of Malcolm Longair's highly appreciated textbook has been extensively and thoroughly updated. It tells the story of modern astrophysical cosmology from the perspective of one of its most important and fundamental problems – how did the galaxies come about? Longair uses this approach to introduce the whole of what may be called "classical cosmology". What’s more, he describes how the study of the origin of galaxies and larger-scale structures in the Universe has provided us with direct information about the physics of the very early Universe.

Man has a great tendency to get lost or to hide, as the case may be, in a jungle of details and in unnecessary complications. Why do anything simply if you can do it complicated? And still, life itself presents a sufficient number of problems to keep us busy. There would seem to be no need to create additional difficulties, just for the fun of it, especially if these self-made difficulties become practically insuperable and if in the end they cause much unhappiness. The morphological mode of thought and of action was conceived to break the vicious hold which the parasitic wild growth of complications exerts on life in all of its phases. Morphological thought and action are likely to be of value in all human activities, once such thought and action have been clearly delineated and fully developed, and once they have been practised by a sufficiently large number of people. Since the morphological method is of the greatest universality, the choice of the field to which one applies it first is not particulary critical. The author intends to write two or three books on the morphology of several large scale problems, which are both of a technical and of a general social nature. The present book is concerned in particular with some implications of morphological thinking in astronomy. We shall above all emphasize the basic character of the morphological approach, and we shall demonstrate its constructive power in a number of specific cases.