Download or read book Constraints on the Shape of Dark Matter in Clusters of Galaxies written by David Augustin Buote and published by . This book was released on 1992 with total page 102 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope written by and published by . This book was released on 2012 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Probing Cosmic Dark Matter and Dark Energy with Weak Gravitational Lensing Statistics written by Masato Shirasaki and published by Springer. This book was released on 2015-11-18 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this book the applicability and the utility of two statistical approaches for understanding dark energy and dark matter with gravitational lensing measurement are introduced. For cosmological constraints on the nature of dark energy, morphological statistics called Minkowski functionals (MFs) to extract the non-Gaussian information of gravitational lensing are studied. Measuring lensing MFs from the Canada–France–Hawaii Telescope Lensing survey (CFHTLenS), the author clearly shows that MFs can be powerful statistics beyond the conventional approach with the two-point correlation function. Combined with the two-point correlation function, MFs can constrain the equation of state of dark energy with a precision level of approximately 3–4 % in upcoming surveys with sky coverage of 20,000 square degrees. On the topic of dark matter, the author studied the cross-correlation of gravitational lensing and the extragalactic gamma-ray background (EGB). Dark matter annihilation is among the potential contributors to the EGB. The cross-correlation is a powerful probe of signatures of dark matter annihilation, because both cosmic shear and gamma-ray emission originate directly from the same dark matter distribution in the universe. The first measurement of the cross-correlation using a real data set obtained from CFHTLenS and the Fermi Large Area Telescope was performed. Comparing the result with theoretical predictions, an independent constraint was placed on dark matter annihilation. Future lensing surveys will be useful to constrain on the canonical value of annihilation cross section for a wide range of mass of dark matter annihilation. Future lensing surveys will be useful to constrain on the canonical value of annihilation cross section for a wide range of mass of dark matter.

Download or read book Modern Cosmology written by Scott Dodelson and published by Academic Press. This book was released on 2003-03-13 with total page 462 pages. Available in PDF, EPUB and Kindle. Book excerpt: An advanced text for senior undergraduates, graduate students and physical scientists in fields outside cosmology. This is a self-contained book focusing on the linear theory of the evolution of density perturbations in the universe, and the anisotropiesin the cosmic microwave background.

Download or read book Connecting Quarks with the Cosmos written by National Research Council and published by National Academies Press. This book was released on 2003-03-12 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances made by physicists in understanding matter, space, and time and by astronomers in understanding the universe as a whole have closely intertwined the question being asked about the universe at its two extremesâ€"the very large and the very small. This report identifies 11 key questions that have a good chance to be answered in the next decade. It urges that a new research strategy be created that brings to bear the techniques of both astronomy and sub-atomic physics in a cross-disciplinary way to address these questions. The report presents seven recommendations to facilitate the necessary research and development coordination. These recommendations identify key priorities for future scientific projects critical for realizing these scientific opportunities.

Download or read book Galactic Dynamics written by James Binney and published by Princeton University Press. This book was released on 2011-10-30 with total page 902 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since it was first published in 1987, Galactic Dynamics has become the most widely used advanced textbook on the structure and dynamics of galaxies and one of the most cited references in astrophysics. Now, in this extensively revised and updated edition, James Binney and Scott Tremaine describe the dramatic recent advances in this subject, making Galactic Dynamics the most authoritative introduction to galactic astrophysics available to advanced undergraduate students, graduate students, and researchers. Every part of the book has been thoroughly overhauled, and many sections have been completely rewritten. Many new topics are covered, including N-body simulation methods, black holes in stellar systems, linear stability and response theory, and galaxy formation in the cosmological context. Binney and Tremaine, two of the world's leading astrophysicists, use the tools of theoretical physics to describe how galaxies and other stellar systems work, succinctly and lucidly explaining theoretical principles and their applications to observational phenomena. They provide readers with an understanding of stellar dynamics at the level needed to reach the frontiers of the subject. This new edition of the classic text is the definitive introduction to the field. ? A complete revision and update of one of the most cited references in astrophysics Provides a comprehensive description of the dynamical structure and evolution of galaxies and other stellar systems Serves as both a graduate textbook and a resource for researchers Includes 20 color illustrations, 205 figures, and more than 200 problems Covers the gravitational N-body problem, hierarchical galaxy formation, galaxy mergers, dark matter, spiral structure, numerical simulations, orbits and chaos, equilibrium and stability of stellar systems, evolution of binary stars and star clusters, and much more Companion volume to Galactic Astronomy, the definitive book on the phenomenology of galaxies and star clusters

Download or read book Particle Dark Matter written by Gianfranco Bertone and published by Cambridge University Press. This book was released on 2010-01-07 with total page 763 pages. Available in PDF, EPUB and Kindle. Book excerpt: Describes the dark matter problem in particle physics, astrophysics and cosmology for graduate students and researchers.

Download or read book Dark Matter in Galaxy Clusters written by Austen M. Groener and published by . This book was released on 2015 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt: We explore the intrinsic distribution of dark matter within galaxy clusters, by combining insights from the largest {\em N}-body simulations as well as the largest observational dataset of its kind. Firstly, we study the intrinsic shape and alignment of isodensities of galaxy cluster halos extracted from the MultiDark MDR1 cosmological simulation. We find that the simulated halos are extremely prolate on small scales and increasingly spherical on larger ones. Due to this trend, analytical projection along the line of sight produces an overestimate of the concentration index as a decreasing function of radius, which we quantify by using both the intrinsic distribution of 3D concentrations ($c_{200}$) and isodensity shape on weak and strong lensing scales. We find this difference to be $\sim 18\%$ ($\sim 9\%$) for low (medium) mass cluster halos with intrinsically low concentrations ($c_{200}=1-3$), while we find virtually no difference for halos with intrinsically high concentrations. Isodensities are found to be fairly well-aligned throughout the entirety of the radial scale of each halo population. However, major axes of individual halos have been found to deviate by as much as $\sim 30^{\circ}$. We also present a value-added catalog of our analysis results, which we have made publicly available to download. Following that, we then turn to observational measurements galaxy clusters. Scaling relations of clusters have made them particularly important cosmological probes of structure formation. In this work, we present a comprehensive study of the relation between two profile observables, concentration ($\mathrm{c_{vir}}$) and mass ($\mathrm{M_{vir}}$). We have collected the largest known sample of measurements from the literature which make use of one or more of the following reconstruction techniques: Weak gravitational lensing (WL), strong gravitational lensing (SL), Weak+Strong Lensing (WL+SL), the Caustic Method (CM), Line-of-sight Velocity Dispersion (LOSVD), and X-ray. We find that the concentration-mass (c-M) relation is highly variable depending upon the reconstruction technique used. We also find concentrations derived from dark matter only simulations (at approximately $\mathrm{M_{vir} \sim 10^{14} M_{\odot}}$) to be inconsistent with the WL and WL+SL relations at the $\mathrm{1\sigma}$ level, even after the projection of triaxial halos is taken into account. However, to fully determine consistency between simulations and observations, a volume-limited sample of clusters is required, as selection effects become increasingly more important in answering this. Interestingly, we also find evidence for a steeper WL+SL relation as compared to WL alone, a result which could perhaps be caused by the varying shape of cluster isodensities, though most likely reflects differences in selection effects caused by these two techniques. Lastly, we compare concentration and mass measurements of individual clusters made using more than one technique, highlighting the magnitude of the potential bias which could exist in such observational samples.Finally, we explore the large-scale environment around galaxy clusters using spectroscopically confirmed galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 10. We correlate the angular structure of the distribution of galaxies (out to a distance of $\mathrm{10 h^{-1}\, Mpc}$) around 92 galaxy clusters with their corresponding mass and concentration measurements. We find that the orientation of the cluster environment on this scale has little impact on the value of cluster measurements.

Download or read book Progress in Dark Matter Research written by J. Val Blain and published by Nova Publishers. This book was released on 2005 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is generally believed that most of the matter in the universe is dark, i.e. cannot be detected from the light which it emits (or fails to emit). Its presence is inferred indirectly from the motions of astronomical objects, specifically stellar, galactic, and galaxy cluster/supercluster observations. It is also required in order to enable gravity to amplify the small fluctuations in the cosmic microwave background enough to form the large-scale structures that we see in the universe today. For each of the stellar, galactic, and galaxy cluster/supercluster observations the basic principle is that if we measure velocities in some region, then there has to be enough mass there for gravity to stop all the objects flying apart. Dark matter has important consequences for the evolution of the Universe and the structure within it. According to general relativity, the Universe must conform to one of three possible types: open, flat, or closed. The total amount of mass and energy in the universe determines which of the three possibilities applies to the Universe. In the case of an open Universe, the total mass and energy density (denoted by the Greek letter Omega) is less than unity. If the Universe is closed, Omega is greater than unity. For the case where Omega is exactly equal to one the Universe is "flat". This book details leading-edge research from around the globe.

Download or read book Shapes Of Galaxies And Their Dark Halos The Proceedings Of The Yale Cosmology Workshop written by Priyamvada Natarajan and published by World Scientific. This book was released on 2002-03-28 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book constitutes the proceedings of a very topical workshop aimed at understanding the shapes of the baryonic and dark matter components of galaxies. Several groups presented their recent results from observations and numerical N-body simulations.

Download or read book On the Distribution of Dark Matter in Clusters of Galaxies written by David Jerome Sand and published by . This book was released on 2006 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Constraining Dark Matter Through the Study of Merging Galaxy Clusters written by William Anthony Dawson and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The majority (~85%) of the matter in the universe is composed of dark matter, a mysterious particle that does not interact via the electromagnetic force yet does interact with all other matter via the gravitational force. Many direct detection experiments have been devoted to finding interactions of dark matter with baryonic matter via the weak force. To date only tentative and controversial evidence for such interactions has been found. While such direct detection experiments have ruled out the possibility that dark matter interacts with baryonic matter via a strong scale force, it is still possible that dark matter interacts with itself via a strong scale force and has a self-scattering cross-section of ~0.5 cm2g−1. In fact such a strong scale scattering force could resolve several outstanding astronomical mysteries: a discrepancy between the cuspy density profiles seen in [Lambda]CDM simulations and the cored density profiles observed in low surface brightness galaxies, dwarf spheroidal galaxies, and galaxy clusters, as well as the discrepancy between the significant number of massive Milky Way dwarf spheroidal halos predicted by [Lambda]CDM and the dearth of observed Milky Way dwarf spheroidal halos. Need: While such observations are in conflict with [Lambda]CDM and suggest that dark matter may self-scatter, each suffers from a baryonic degeneracy, where the observations might be explained by various baryonic processes (e.g., AGN or supernove feedback, stellar winds, etc.) rather than self-interacting dark matter (SIDM). In fact, the important scales of these observations often coincide with baryonic scales (e.g., the core size in clusters is few factors smaller than the radius of the brightest cluster galaxy). What is needed is a probe of SIDM where the expected effect cannot be replicated by the same processes responsible for the baryonic degeneracy in the aforementioned probes. Merging galaxy clusters are such a probe. During the merging process the effectively collisionless galaxies (~2% of the cluster mass) become dissociated from the collisional intracluster gas (~15% of the cluster mass). A significant fraction of the gas self-interacts during the merger and slows down at the point of collision. If dark matter lags behind the effectively collisionless galaxies then this is clear evidence that dark matter self-interacts. The expected galaxy-dark matter offset is typically >25 kpc (for cross-sections that would explain the other aforementioned issues with [Lambda]CDM), this is larger than the scales of that are plagued by the baryonic degeneracies. Task: To test whether dark matter self-interacts we have carried out a comprehensive survey of the dissociative merging galaxy cluster DLSCL J0916.2+2951 (also known as the Musket Ball Cluster). This survey includes photometric and spectroscopic observations to quantify the position and velocity of the cluster galaxies, weak gravitational lensing observations to map and weigh the mass (i.e., dark matter which comprises ~85% of the mass) of the cluster, Sunyaev-Zel'dovich effect and X-ray observations to map and quantify the intracluster gas, and finally radio observations to search for associated radio relics, which had they been observed would have helped constrain the properties of the merger. Using this information in conjunction with a Monte Carlo analysis model I quantify the dynamic properties of the merger, necessary to properly interpret constraints on the SIDM cross-section. I compare the locations of the galaxies, dark matter and gas to constrain the SIDM cross-section. This dissertation presents this work. Findings: We find that the Musket Ball is a merger with total mass of 4.8(+3.2)(-1.5) x 1014M(sun). However, the dynamic analysis shows that the Musket Ball is being observed 1.1(+1.3)(-0.4) Gyr after first pass through and is much further progressed in its merger process than previously identified dissociative mergers (for example it is 3.4(+3.8)(1.4) times further progressed that the Bullet Cluster). By observing that the dark matter is significantly offset from the gas we are able to place an upper limit on the dark matter cross-section of [sigma](SIDM)m−1(DM)

Download or read book Dark Energy Survey The The Story Of A Cosmological Experiment written by Ofer Lahav and published by World Scientific. This book was released on 2020-08-19 with total page 445 pages. Available in PDF, EPUB and Kindle. Book excerpt: 'The past cultures of astronomy and physics evolved their own distinct personalities. The book describes an important milestone in the history of the unification of the two fields and provides an excellent summary of the methods used to explore one of the greatest mysteries in physics today: dark energy.'Physics TodayThis book is about the Dark Energy Survey, a cosmological experiment designed to investigate the physical nature of dark energy by measuring its effect on the expansion history of the universe and on the growth of large-scale structure. The survey saw first light in 2012, after a decade of planning, and completed observations in 2019. The collaboration designed and built a 570-megapixel camera and installed it on the four-metre Blanco telescope at the Cerro Tololo Inter-American Observatory in the Chilean Andes. The survey data yielded a three-dimensional map of over 300 million galaxies and a catalogue of thousands of supernovae. Analysis of the early data has confirmed remarkably accurately the model of cold dark matter and a cosmological constant. The survey has also offered new insights into galaxies, supernovae, stellar evolution, solar system objects and the nature of gravitational wave events.A project of this scale required the long-term commitment of hundreds of scientists from institutions all over the world. The chapters in the first three sections of the book were either written by these scientists or based on interviews with them. These chapters explain, for a non-specialist reader, the science analysis involved. They also describe how the project was conceived, and chronicle some of the many and diverse challenges involved in advancing our understanding of the universe. The final section is trans-disciplinary, including inputs from a philosopher, an anthropologist, visual artists and a poet. Scientific collaborations are human endeavours and the book aims to convey a sense of the wider context within which science comes about.This book is addressed to scientists, decision makers, social scientists and engineers, as well as to anyone with an interest in contemporary cosmology and astrophysics.Related Link(s)

Download or read book Applications of Weak Gravitational Lensing written by Candace Oaxaca Wright and published by . This book was released on 2002 with total page 376 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Probabilistic Inference of Dark Matter Properties in Galaxy Clusters and the Cosmic Web written by Yin-Yee Ng and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Mass tells spacetime how to curve, spacetime tells mass how to move". This famous quote by physicist John Archibald Wheeler succinctly summarizes General Relativity, the most successful theory that describes our universe at large scale. However, most of the mass that General Relativity describes, namely dark matter (DM), remains a mystery. We have solid evidence of the existence of DM from various observations, but we know little or nothing about the particle nature of DM and how DM particles interact with different particles. Completing this knowledge gap would improve or revolutionize our established cosmological model, the Lambda Cold-Dark Matter (CDM) model, and give directions to theories beyond the standard particle physics model.This work attempts to study DM by examining and extending existing modeling approaches of DM and its visible tracers in a probabilistic way. The single verified form of DM interaction is gravitational. Currently, the only way to infer the properties of DM is through visible tracers. Most of these indirect detections either have low signal-to-noise, sparse coverage, or missing variables. These limitations introduce additional modeling choices and uncertainties. A probabilistic approach allows us to propagate the uncertainties appropriately and marginalize any missing variables. There are two recurring types of visible tracers that my work uses. The first type of tracers are galaxies and observables in the overdense regions of DM. These tracers allow usto infer the macroscopic dynamical properties of DM distribution that we want to study. The second type of tracers, on the hand, are in the background, i.e. further away than the foreground dark matter, from us observers. The gravity of DM can bend spacetime such that the path of light traveling in the vicinity would also curve, leaving distortions in the galaxy images. The gravitational distortion of the images of the background galaxies is also known as gravitational lensing. In the introduction (first chapter) of this thesis, I will layout the technical history, terminology and the reasons behind choosing the various data sets and give an overview of the analysis methods for my thesis work. In chapter two, I will present the study based on the observational data of El Gordo, one of the most massive, most ancient, merging galaxy clusters. Under the extreme collision speeds during a merger of a galaxy cluster, it is more probable for DM particles in the cluster to manifest eects of self-interaction. Thus, if DM particles can interact with one another, some preliminary simulations have shown that large-scale spatial distribution of DM can show discrepancies from its galaxy-counterparts. This discrepancy is also known as the galaxy-DM offset, with a caveat. The long duration (millions of years) of a merger means that we cannot detect the direction of motions of the components directly to confirm the offset as a lag. My work on El Gordo was the first to show a quantitative method of estimating how likely the DM components of El Gordo are to be moving in a certain direction. This study was made possible by utilizing informative observables in various wavelengths, including a pair of radio shockwaves on the outer skirt of the cluster, enhanced X-ray emissivity and the decrement of the Sunyaev-Zel'Dovich effect for the infra-red observations. This comprehensive set of observables allowed us to formulate probabilistic constraints in our Monte Carlo simulation of El Gordo. Furthermore, the study also brought up several questions about the modeling choices for comparing the DM and the member-galaxy distributions of a cluster. For instance, do the DM maps and the galaxy maps have high enough resolution to show the delicate offset signal produced by the possible self-interaction of DM (SIDM)? To address my concerns from the study of El Gordo, I conducted a second investigation of galaxy clusters in a cosmological simulation, which is described in chapter 3. The dataset I chose was from the Illustris simulation. As this simulation assumes a Cold-Dark-Mattermodel (CDM) without requiring an SIDM model, any offset between DM and the member galaxies in a galaxy cluster provides an estimate of the variability of the galaxy-DM offset. My study shows that the variability in this setting is non-negligible compared to the small observed offsets, it is likely that random variation can account for the galaxy-DM offsets inobservations. The result weakens our belief that SIDM is the cause of the offsets. The fourth chapter of my dissertation builds on top of my previous experience with analyzing the weak lensing data for El Gordo. This time, I performed the weak lensing study for a dataset of a much larger spatial scale, such that, galaxy clusters look like parts of a homogeneous and isotropic DM web. At this scale, it is possible to compare the spatial distribution of DM to simulations to give competitive constraints on cosmological parameters. Using weak lensing signals for estimating cosmological parameters is also known as cosmic shear inference. While I used a parametric technique to estimate the mass of El Gordo in chapter 2, my work in chapter 4 introduces a new non-parametric model using a Gaussian Process. A Gaussian Process is a generalization of the multivariate normal distribution to higher dimensions. We can draw functional models from a Gaussian Process to describe our data. While the realizations are drawn from a multivariate normal distribution, we can specify the parameters and the functional structure of the covariance (kernel) matrix of the underlying distribution. This generative model gives us the ability to put probabilistic estimates of DM density in regions without any background galaxies. As I have built the lensing physics into the very core of the covariance kernel matrix, we can also simultaneously infer the several important lensing observables, such as shear and convergence, given some lensed galaxy shapes. More importantly, this technique relies on fewer assumptions about the photometric redshift than traditional cosmic shear analysis technique. This may reduce the bias towards a ducial cosmology and lead to interesting discoveries. However, this new technique is not without its challenges. Computationally, this technique requires an O(n3) runtime. Despite my best attempts to parallelize the computation, the algorithm takes longer for generating DM mass maps than traditional approaches. My work here marks the beginning of an alternative method for cosmic shear inference. Many promising approximation techniques have emerged to drastically speed up the runtime of doing inference with a Gaussian Process. Incorporating these approximations may make it possible to use this method to give tighter cosmological constraints from future sky surveys such as the Large Synoptic Survey Telescope. I conclude my work in Chapter 5 and discuss the implications of my work. This includes some future directions for analyzing DM by using simulations with different underlying DM models and real data.

Download or read book Dark Matter Halos and Stellar Kinematics of Elliptical Galaxies written by Jeremy David Murphy and published by . This book was released on 2012 with total page 606 pages. Available in PDF, EPUB and Kindle. Book excerpt: The hierarchical assembly of mass, wherein smaller clumps of dark matter, stars, gas, and dust buildup over time to form the galaxies we see today in the local Universe through accretion events with other clumps, is a central tenet of galaxy formation theory. Supported by theoretically motivated simulations, and observations of the distribution of galaxies over a large range of redshift, the theory of hierarchical growth is now well established. However, on the scales of individual galaxies, hierarchical growth struggles to explain a number of observations involving the amount and distribution of dark matter in galaxies, and the timescale of both the formation of stars, and the assembly of those stars into galaxies. In this dissertation I attempt to address some of the central issues of galaxy formation. My work focuses on massive elliptical galaxies and employs the orbit-based, axisymmetric dynamical modeling technique of Schwarzschild to constrain the total mass of a galaxy to large radii. From this starting point a determination of the extent and shape of the dark matter halo profile is possible and can then be compared to the results of simulations of the formation of galaxies. These dynamical models include information on the stellar orbital structure of the galaxy, and can be used as a further point of comparison with N-body simulations and observations from other groups. Dynamical modeling results for both M49 and M87, the first and second rank galaxies in the Virgo Cluster, are presented and compared in Chapters 4 and 2 respectively. Although both galaxies are similar in mass, a closer analysis shows they exhibit very different dark matter halo profiles and stellar orbital structure, and likely followed very different formation pathways. My primary dataset comes from observations carried out on the Mitchell Spectrograph (formally VIRUS-P) at McDonald Observatory.\footnote{The instrument's name was changed over the last year. As some of this work was originally written when the instrument was named VIRUS-P, I have elected to use that name in those sections of this dissertation (Chapters 2 and 5). In Chapters 3, 4, and 6, I use the current name.} The Mitchell Spectrograph is a fiber-fed integral field spectrograph, and allows one to collect spectra at many positions on a galaxy simultaneously. With spectroscopy one is able to not only constrain the kinematics of the stars, but also their integrated chemical abundances. In the introduction I describe recent work I have carried out with my collaborators using the Mitchell Spectrograph to add further constraints to our picture of galaxy formation. In that work we find that the cores of massive elliptical galaxies have been in place for many billions of years, and had their star formation truncated at early times. The stars comprising their outer halos, however, come from less massive systems. Yet unlike the stars of present day, low-mass galaxies, whose star formation is typically extended, these accreted systems had their star formation shut off at high redshift. Although our current sample is relatively small, these observations place a rigid constraint on the timescale of galaxy assembly and indicate the important role of minor mergers in the buildup of the diffuse outer halos of these systems. All of these advances in our understanding of the Universe are driven, in large part, by advances in the instrumentation used to collect the data. The Mitchell Spectrograph is a wonderful example of such an advance, as the instrument has allowed for observations of the outer halo of M87 to unprecedented radial distances (Chapter 3). A significant component of my dissertation research has been focused on characterizing the fiber optics of both the Mitchell Spectrograph and the fiber optics for the VIRUS spectrograph. I cover the results of the work on the Mitchell Spectrograph optical fibers in Chapter 5. The affects of stress and motion on a fiber bundle, critical to the VIRUS spectrograph, are explored in Chapter 6.

Download or read book Cosmological Aspects of X Ray Clusters of Galaxies written by W.C. Seitter and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt: The NATO Advanced Study Institute "Cosmological Aspects of X-Ray Clus ters of Galaxies" took place in Vel en , Westphalia, Germany, from June 6 to June 18, 1993. It addressed the fruitful union of two topics, cosmology and X-ray clus ters, both of which carry substantial scientific weight at the beginning of the last decenium of the last century in the second millenium of our era. The so far largest X-ray "All-Sky Survey", observed by the ROSAT X-ray satel lite, and ROSAT's deep pointed observations, have considerably enlarged the base of X-ray astronomy, particularly concerning extragalactic sources. Cosmology has gained significant impetus from the large optical direct and spectroscopic surveys, based on high quality 2-dimensional receivers at large telescopes and powerful scan ning devices, harvesting the full information 1 content from the older technique of employing photographic plates. Radioastronomy and IR-astronomy with IRAS, as well as r-astronomy with GRO, continue and strengthen the role of extragalactic research. The rapidly growing computer power in data reduction and data storage facilities support the evolution towards large-number statistics. A most significant push was given to early cosmology by the needs of physics in trying to unravel the nature of forces which govern our material world. The topic of the ASI was chosen because it opens new vistas on this for ever new problem: the universe. Clusters of galaxies probe large-scale matter distributions and the structure of space-time.