Proceedings of the NATO Advanced Study Institute, Les Houches, France, March 20-30, 1991

"Astronomy and Astrophysics Abstracts" appearing twice a year has become oneof the fundamental publications in the fields of astronomy, astrophysics andneighbouring sciences. It is the most important English-language abstracting journal in the mentioned branches. The abstracts are classified under more than a hundred subject categories, thus permitting a quick survey of the whole extended material. The AAA is a valuable and important publication for all students and scientists working in the fields of astronomy and related sciences. As such it represents a necessary ingredient of any astronomical library all over the world.

IAU Symposium No. 168, Examining the Big Bang and Diffuse Background Radiations, took place on August 23-26, 1994 at the XXIInd IAU General Assembly in the Hague, Netherlands. The meeting attracted a large number - over 250 - of astronomers, reflecting the strong interest engendered by the great advances in cosmology made in recent years. There is still a multitude of unresolved problems in modern cosmology and the symposium offered a wonderful occasion to examine them objectively, at a place where many leading workers in related fields gathered together. After the introduction by IAU President L. Woltjer and the historical background by Vice Present Virginia Trimble, the volume begins with reviews of the cosmic microwave radiation from COBE (Cosmic Background Explorer). Reviews of recent observations then extend from radio to infrared, visible light, ultraviolet, X-rays and gamma-rays. It is followed by theoretical models for the Big Bang and Inflation, and alternative views to the Big Bang. Following a discourse on Probes and Future Tests, the meeting ended with a Panel Discussion on `Major Unsolved Problems of Cosmology'. Some forty-four contributed papers - both oral and poster reports - are included after the invited talks and panel discussions.

The Sixth Moscow Quantum Gravity Seminar was a continuation of the series of seminars which has played an important role in the consolidation of the international quantum gravity community and which has greatly affected the development of the field. As well as papers presented at the conference, this proceedings volume includes the papers of invited speakers who were unable to attend the seminar itself.

This book reviews the interconnection of cosmology and particle physics over the last decade. It provides introductory courses in supersymmetry, superstring and M-theory, responding to an increasing interest to evaluate the cosmological consequences of these theories. Based on a series of extended courses providing an introduction to the physics of the very early universe, in the light of the most recent advances in our understanding of the fundamental interactions, it reviews all the classical issues (inflation, primordial fluctuations, dark matter, baryogenesis), but also introduces the most recent ideas about what happened at the Big Bang, and before.

An up-to-date presentation of the progress and current problems in the early universe, cosmic microwave background radiation, large scale structure formation, and the interplay between them. The emphasis is on the mutual impact of fundamental physics and cosmology, both at theoretical and experimental (observational) levels within a deep, well- focused and well-defined programme. The nature of the domain itself leads to different aspects, approaches and points of view on the same topic. Special care has been taken to provide the reader the basis of the different, sometimes competing lines of research. All contributions are uniformly excellent, with a careful selection of the subjects and approaches covered, presenting a unifying and rigorous view of the field. Audience: experimentalists and theoreticians from a variety of backgrounds: physics, astrophysics and astronomy. An excellent reference for post-doctoral scientists. Useful for senior scientists and advanced graduate students.

This study is devoted to the Sunyaev-Zeldovich (S-Z) effect, and important related topics in cluster and CMB research. S-Z science is about to be significantly enhanced by unique, multi-faceted cluster and cosmological yield, at a level of precision in accord with the high standards of the current era that was heralded by spectacular achievements in cosmological CMB research. The pedagogical reviews and technical seminars included in this volume represent most of the important current topics in S-Z work and in the astrophysics of clusters. The publication touches upon all relevant aspects of the S-Z effect and its use as a precise cluster and cosmological probe. To commemorate the 40th anniversary of the detection of the CMB by Penzias and Wilson (in 1964), there is a chapter devoted to the history of this discovery. In his fascinating account of their work, he outlines also some lessons pertinent to current scientific issues. Other chapters discuss very interesting related observational work in Europe and the US.

ROSAT Observations G. HASINGER Max-Planck-Institut flir extraterrestrische Physik, D-85740 Garching, Germany Abstract. This review describes the most recent advances in the study of the extragalactic soft X-ray background and what we can learn about its constituents. The deepest pointed observations with the ROSAT PSPC are discussed. The logN-logS relation is presented, which reaches to the faintest X-ray fluxes and to the highest AGN surface densities ever achieved. The N(>S) relation shows a 2 density in excess of 400 deg- at the faintest fluxes and a flattening below the Einstein Deep Survey limit. About 60% of the extragalactic background has been resolved in the deepest field. Detailed source spectra and first optical and radio identifications will be discussed. The results are put into perspective of the higher energy X -ray background. Key words: X-rays, background radiations, active galactic nuclei. 1. Introduction The extragalactic X-ray background (XRB), discovered about 30 years ago, has been studied extensively with many X-ray experiments, in particular with the satel lites HEAO I and II (see ego Boldt 1987) and with ROSAT (e. g. Hasinger et aI. , 1993). Figure 1 shows a compilation of some of the most recent spectral measure ments for the X-ray background. Over the energy range from 3 to about 100 keY its spectrum can be well approximated by an optically thin thermal bremsstrahlung model with kT ~ 40 keY, while at lower X-ray energies a steepening into a new component has been observed observed (e. g.