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We develop the properties of cosmological many-body clustering at high redshift and compare the resulting theoretical distributions with recent observations of groups of galaxies around z ≈ 3. Analyses of the observed variance of counts-in-cells and of the probability for forming strongly overdense regions suggest Ω0 ≈ 0.3 ± 0.2 and 0.1 Ω0 0.3, respectively, for Einstein-Friedmann universes. Since these models are essentially analytical, they allow us to examine statistical questions that have analogs in more complicated cold dark matter models based on small numbers of simulations. We show how future observations of the galaxy distribution function can test cosmological many-body clustering and determine Ω0 more precisely. For Ω0 0.3, these models predict that galaxies start clustering at redshifts z 10.

We analyze the three-dimensional spatial-velocity distribution of the counts-in-cells for 4501 galaxies in the Pisces-Perseus supercluster. This is done for the total sample, for a subset containing the most conspicuous galaxies (brightest members with large intrinsic linear diameters), and for a subset contain- ing the least conspicuous galaxies (faintest members with small intrinsic linear diameters). We also examine subsets limited by absolute magnitudes as well as volume limited samples. The counts-in-cells distribution functions for all these samples are described remarkably well by the gravitational quasi- equilibrium distribution which was previously found to -t the more statistically homogeneous Zwicky, CfA, ESO, and IRAS catalogs. For the complete Pisces-Perseus sample, the value of b, representing the ratio of gravitational correlation energy to the kinetic energy of peculiar motions is 0.8. The most con- spicuous galaxies are somewhat more uniformly distributed than the least conspicuous ones which tend to follow the overall distribution. A dendrogram analysis shows that groups of the most conspicuous galaxies tend to be located near groups of the least conspicuous ones. We also analyze the velocity distribution in di†erent parts of the supercluster. There is a dense core of about 750 galaxies which have an overall Gaussian velocity distribution with a dispersion of about 450 km s~1 around the mean of 5260 km s~1. However this region is not completely relaxed since it con- tains subgroups which may not have Gaussian distributions. Moreover, in most subgroups the crossing time exceeds the Hubble time, indicating incomplete relaxation. Irregular galaxies tend to concentrate in this region, perhaps indicating signi-cant tidal interactions. Spatial distribution functions measured for increasing numbers of galaxies around the dense core of Pisces-Perseus approach the form and have the value of b observed in larger statistically homogeneous catalogs. It appears that galaxies in this region constitute a "" fair sample II with a wide range of Z103 structures characteristic of gravitational clustering. Our results appear consistent with the supercluster forming gravitationally as an accumulation of smaller clusters. Accurate peculiar velocities of these galaxies would help decide whether this clustering was stimulated by a larger scale perturbation or occurred by chance. Subject headings: galaxies: clusters: individual (Pisces-Perseus) E gravitation

We study how merging affects the luminosity and the spatial distributions of galaxies. By using a master equation description and a distribution of physical merging cross sections, we find that the evolution of the galaxy luminosity distribution and the spatial counts-in-cells distribution are closely related. They place strong constraints on each other. The observed evolution of the galaxy luminosity function in the Autofib Redshift Survey (Ellis et al.) implies at least a 10% decrease in the galaxy comoving number density at z < 0.7. This significantly affects the evolution of galaxy spatial counts-in-cells distribution. The observed evolution of the galaxy luminosity function also requires a form of "differential dimming" for the less luminous galaxies even if galaxy merging drives the evolution. A counts-in-cells analysis for distant galaxies would help clarify the nature of the excess counts of faint-blue galaxies at high redshifts.

Even before astronomers knew that galaxies existed, they found that they are clustered. Though this statement may seem contradictory, it is not quite as contradictory as it seems. In compiling his famous catalog of nebulae, Messier (1781) noticed that about a dozen of his hundred or so objects were clumped together in the constellation of Virgo. A few years later, William Herschel (1784, 1811) sweeping the heavens with his telescope in Slough, recognized great inhomogeneities in the distribution of his much larger collection of thousands of nebulae. Herschel speculated, as Hubble and others would show definitively in the 1920s, that many of these nebulae were vast star systems, like our own Milky Way, held together and perhaps even caused to cluster by the forces of gravity. Most of Messier’s objects in Virgo were, in fact, such galaxies.

If I were a good first-year physics undergraduate, I'd run out and buy this book, impelled by the author's enthusiasm. There is no disputing the extraordinary advances in our understanding of astrophysics and cosmology made over the last three decades – since about the time Malcolm Longair began contributing to them. He has now written a coherent, generally accurate and always optimistic overview of much of the most exciting modern astrophysics. The book concentrates on the formation and evolution of stars, the nature and origins of galaxies and quasars, and the origin of the universe. All these make a continuous story, told at the level of an elementary textbook and oriented toward physical explanations. It is also beautifully illustrated. This book would be an excellent choice for anyone who has a qualitative understanding of basic physics and wants an introduction to recent developments in astronomy.

We describe a simple general objective method for determining the distribution functions (counts in cells) of biased subsamples. This method does not depend on any specific definition of a "cluster." Applying this to morphological subsets of the UGC and ESO catalogs, and to the IRAS catalog, quantifies the excess clustering of early-type E + SO galaxies relative to Sa + Sb spirals. Spirals are distributed nearly randomly, while the average probability of finding an elliptical in a region containing M galaxies is p(M) approximately M0.3.If the present galaxy distribution is similar to the distribution when stripping and merging occurred, then these processes do not account for the observed morphology-density relation of ellipticals and spirals. Models in which stripping or merging occurred at high redshifts are constrained by the requirement that they evolve into the presently observed distribution functions of ellipticals and spirals, which are consistent with simple gravitational clustering. These morphology-density relations may be consistent with gravitational segregation if the average masses associated with ellipticals are several times greater than those of spirals. It may also reflect the initial density threshold for different galaxy types.

The paper examines the structure present on scales of 10-50 Mpc in the Abell cluster catalog and on scales of about 100 Mpc in a new complete catalog of 297 radio sources with fluxes greater than 5 mJy in a 4 x 4 degree area. The analysis employs the f(N) distribution, which measures the probability of finding N objects in a given volume or area of sky. The Abell catalog f(N) distribution is consistent with the f(N) distribution for gravitational clustering. Modifications of the Abell catalog and some artificially generated catalogs are examined to explore possible selection effects, and the observed results appear to be quite robust. The results imply that the initial conditions for the formation of structure were Poisson on large scales. 33 refs.

Observations of a new type of rapidly varying radio source have recently been reported1. The principal characteristics of the four sources so far discovered may be summarized as follows—sharp pulses of radiation are received, separated by comparatively long intervals which themselves are remarkably constant (with variations of ≲ 1 part in 2 × 107 during the past 3 or 4 months). The pulse duration is no more than ~ 0·016 s, while the period is 1#x00B7;3372795 ±0#x00B7;0000020 s (ref. 1). We understand that the other objects show similar sharp pulses at intervals of the order of 1 s, which, although not identical, strongly suggest that a new type of physical system has been discovered. Hewish et al. propose that the objects may be pulsating white dwarfs or neutron stars. Although this may prove to be correct, there are certain difficulties associated with the constancy of the observed period. We suggest an alternative explanation for the observed phenomena.

During the collapse of pre-galactic gas clouds through a density of about 104 particles/cm3, hydrogen molecules are produced and dominate the subsequent cooling.

NONE of the classical models for the interstellar dust grains fit in with all the modern observations. Pure graphite particles produce insufficient extinction in the far ultraviolet1. The strong absorption band in the infrared predicted for ice or ice-coated graphite particles is not observed2. Neither type of particle has the combined properties of high albedo and nearly isotropic phase function needed to fit the observations of the diffuse galactic radiation3. These difficulties would be eliminated if the dust grains contain an abundant element in an allotropic form not considered previously: carbon in the form of diamond.