Galaxy groups and clusters provide excellent laboratories for studying galaxy properties in different environments and at different look-back times. In particular, the recent detections of high-redshift cluster candidates, only possible with the current high-technology instrumentation, add a new dimension to the problem. Along with the ever increasing computing power and sophisticated algorithms to model clusters of galaxies, it may help us to understand the origins of today's groups and clusters, as well as of their member galaxies. These workshop proceedings provide a snapshot of the current research in this subject, covering the observations, theory and numerical simulations relevant to galaxy evolution in groups and clusters. In this book, intended primarily to researchers in the field, particular emphasis is given to the recent impressive progress in the field, on important new results, and on the future prospects and open questions to be tackled.

Bulges lie at the heart of most galaxies, the building blocks of our universe. With a selection of reviews and topical presentations, IAU Symposium 245 provides an up-to-date overview of our knowledge on galaxy bulges, and a concise introduction to all current research on the subject. The structure, dynamics, and stellar populations of galaxy bulges, both near and far, are analysed through state-of-the-art observations. The leading models for the formation and evolution of galaxy bulges are described in detail, and the constraints observations put on these are dissected. Particular emphasis is placed on exploring evidence for both hierarchical merging and secular processes. Special attention is also devoted to disentangling the complex web relating galaxy bulges and central supermassive black holes, and on the lessons learned from our exquisite knowledge of the bulge of our own Milky Way. This volume is the best one-stop reference on galaxy bulges currently available.

Bulges lie at the center of spiral galaxies. Until recently, they were thought to host uniquely old stellar populations and thus provide a key for understanding galaxy formation. Recent observations from the ground and space have drastically changed our view on the nature of bulges and shown that they can also contain dust, gas, and star-forming regions. This timely volume presents review articles by a panel of international experts who gathered at a conference at the Space Telescope Science Institute, Baltimore, to address several fundamental questions: What is a bulge? When and how did bulges form? And, on what timescales? This volume provides a state-of-the-art picture of our new understanding of these fundamental building-blocks of galaxies, and a stimulating reference point for all those interested in galaxy formation.

Globular clusters are a class of very old, massive, spherical, gravitationally bound star cluster which likely play an important, but as of yet unknown, role in the formation and evolution of galaxies. These clusters had been regarded as the archetypical example of simple stellar populations, with all stars having been born at the same time from the same star-forming gaseous material. One of the major predictions of such a model is that the stars in the cluster should have identical abundances, save for inhomogeneities caused by self-enrichment of red giant atmospheres via mixing of material processed in the inner layers of the evolved stars up to their surface. However, in several pivotal studies at the turn of the 21st century, star-to-star variations in atmospheric chemical abundance were discovered among unevolved stars on the main sequence of several Galactic globular clusters, prompting acceptance of a multiple populations model. It has since been demonstrated that almost all Galactic globular clusters harbor multiple populations. Several of the most popular models envision a first generation of stars forming in the protocluster with primordial abundances, followed by formation of a second generation out of intracluster material polluted with light element products of the CNO cycle (along with the NeNa- and MgAl-chain) processes. In these scenarios, the ejecta of SNe, which include Fe and other heavy elements, attains escape velocity and does not contribute to the abundances of the second generation. However, the complexity of the observed chemical trends has so far eluded comprehensive explanation, and there is still no unified model for the origin of multiple populations in globular clusters.In this dissertation, we seek to provide key constraints on competing models of the origin of multiple populations in globular clusters by studying the relative fraction of stars of different generations, and their distribution, among 14 inner Milky Way clusters which span a wide range in mass, dynamical age, and orbital characteristics. This work was made possible by use of the Blanco DECam Bulge Survey point source catalog, providing deep, wide-field, NUV-NIR broadband photometry for more than 250 million stars toward the southern Galactic bulge. Proper motions for many of the stars were available after cross-matching the photometric catalog with Gaia EDR3, which allowed for the creation of high resolution extinction maps toward the target clusters. The extinction maps allowed us to correct the photometry for the effects of differential reddening, which can be quite severe toward the Galactic bulge. By taking advantage of the de-reddened u-band, we showed that the Blanco photometry is capable of separating cluster red giant stars based on their N (Na) abundance, enabling wide-field studies of the populations in these clusters with large number statistics. With this preferentially metal-rich sample, we were able to test whether the well-known correlations between the properties of the populations and their parent clusters hold true at higher metallicity. We were also able to compare wide-field distributions of the cluster multiple populations with orbital and internal dynamical properties of the parent clusters, which are on preferentially disruptive orbits, in order to test dynamical models of the evolution of multiple populations.

This book consists of invited reviews on Galactic Bulges written by experts in the field. A central point of the book is that, while in the standard picture of galaxy formation a significant amount of the baryonic mass is expected to reside in classical bulges, the question what is the fraction of galaxies with no classical bulges in the local Universe has remained open. The most spectacular example of a galaxy with no significant classical bulge is the Milky Way. The reviews of this book attempt to clarify the role of the various types of bulges during the mass build-up of galaxies, based on morphology, kinematics and stellar populations and connecting their properties at low and high redshifts. The observed properties are compared with the predictions of the theoretical models, accounting for the many physical processes leading to the central mass concentration and their destruction in galaxies. This book serves as an entry point for PhD students and non-specialists and as a reference work for researchers in the field.