The intent of this brief note is to summarize some of the fundamental properties of the region, rich in galaxies, in which we live. A more complete account can be found in The Astrophysical Journal, 257, p. 389, 1982.

The spatial distribution of galaxies in the Local Supercluster, as described at this meeting, together with the measured anisotropy in the microwave background suggest that there exist significant deviations from a uniform Hubble flow in the velocity field of galaxies within a few thousand km/s. In principle, it is not too hard to improve on the uniform flow model: one simply needs to examine the spatial distribution of the radial velocity residuals for many nearby galaxies. In practice, the problem is non-trivial because of the coupling of velocity and distance, and the lack of a distance indicator of high precision, and the “thermal” noise in the velocity field. Our recent efforts in this direction are described in more detail in a paper in a current Astrophysical Journal (Aaronson et al. 1982a).

The formation of aspherical superclusters (SC's) is studied by 3-D N-body simulations that are confronted with the Local SC (LSC), and a simple model is developed. A nondissipative scenario, in which galaxies are formed from perturbations on smaller scales prior to the collapse of SC's, is found to be successful. It explains the disk-halo structure of SC's, their flattening and their low dispersions, which are nontransient because of the expansion along the long axes. The LSC has collapsed at z≤0.5. The large-scale velocity isotropy and the local 1-D infall indicate Ω<1. The correlation of galaxies on a few Mpc scales grows nonselfsimilarly due to recent pancaking rather than gradual clustering. This may be tested by the lack of clustering among objects at z>1.

A measurement of the motion of the Local Group of galaxies through the Universe provides an indication of their peculiar motion relative to the Hubble flow consequent upon the gravitational influence of the local large scale mass inhomogeneities. This motion can be measured either relative to the cosmic microwave background at z ∼ 1000 or relative to the background or nearby (z ∼ 0.01) galaxies. The interpretation of published measurements is subject to some uncertainty. As an example, the Local Group motion derived from optical studies of nearby galaxies (Rubin et al. 1976) differs from that derived from radio frequency measurements of the dipole anisotropy in the microwave background. (Boughn et al. 1981, Gorenstein & Smoot 1981).

There are a subtantial number of galaxies in the Virgo southern extention just beyond the Virgo Cluster which are blueshifted with respect to the cluster and a lesser number of galaxies slightly nearer than the Virgo Cluster which are redshifted with respect to the cluster. These galaxies must be falling into the cluster. We are able to model the observed infall motions by following the collapse of spherical shells with the Friedmann equations in a closed universe. A family of mass-age solutions provide satisfactory fits to the observations.

Environmental effects may be of great importance to the structure and evolution of galaxies. Sullivan and collaborators (1981, AJ 86, 919) find that the ratio between HI content and luminosity of galaxies tends to be smaller in regions of high galaxy density than elsewhere. It is not quite clear what processes reduce the gas content (or enhance the luminosity!): collisions, mergers or tidal interactions of galaxies, encounters with gas clouds, stripping by ram pressure? Detailed comparison of gas distributions and motions in cluster and field galaxies may help answer this question.

By using the two samples of galaxy groups reselected by Rood and Dickel (1979, Astroph. J. 233, 418), we have investigated the significance of the correlations between the virial parameters of groups. Taking into account observational selection effects present in the two samples, together with statistical and observational uncertainties, we show that only an intrinsic correlation between the luminosity L and velocity dispersion V is necessarily required in order to explain all the observed correlations. There is no serious ground to state that the virial radius correlates with both velocity dispersion and luminosity. We also show that the observed slope of the Log L - Log V relation is considerably smaller than the true slope, while the contrary holds for the Log M/L - Log V relation.

An analysis similar to that described above, carried on the recent catalogue of nearby groups of galaxies prepared by Huchra and Geller (1982, Astroph. J. 257, 423), seems to reveal that also the intrinsic correlations between L and R, and R and V are significant for this new sample.

So far the galaxy correlation analysis was the only quantitative method used to describe the distribution of galaxies in space. Here we consider other numerical methods to treat impersonally various aspects of the galaxy distribution.

In analyzing the distribution of galaxies of a sample projected on the plane of the sky, the magnitude of a surface density enhancement produced by a clumpy structure depends on the size and magnitude of the volume density enhancement, and the depth of the sample. If the sample is too deep, or the line of sight size or volume overdensity of the clump too small, the surface enhancement may be too shallow to discern against the fore- and background objects. The Catalogue of Galaxies and Clusters of Galaxies (CGCG: Zwicky et al. 1960–68) provides a representative sample of the local universe (cz ≤ 15000 km s−1) and, in hindsight, possibly the one available that best enhances the inhomogeneities that appear to characterize the large scale structure of the universe. Using maps of the surface density distribution of galaxies from the CGCG, of which figure 1 is an example, Martha Haynes, Guido Chincarini and I have selected a number of filamentary structures discernable and undertaken a 21 cm redshift survey of large regions enclosing them, with the telescopes of 305 m at Arecibo and 92 m at NRAO-Green Bank. Here I shall discuss our current results from a large area extending from Pegasus to Ursa Major, which engulfs the well known Perseus supercluster (Einasto et al. 1980; Gregory et al. 1981).

The Ursa Major supercluster is an association of ten Abell clusters which lie within 7° of each other. The center of the system has equatorial coordinates RA (1950.0) and galactic coordinates l = 143°, b = 60°.

Redshifts of clusters of galaxies have been obtained in four regions of the sky selected as suspected rich superclusters at intermediate redshift (0.1 < z < 0.3). Measurements to date have detected the existence of several superclusters with dimensions up to 50 h−1 Mpc (h = H0/100 k/s/Mpc), irregular shapes, and containing as many as seven rich clusters in the richest supercluster. The velocity dispersions suggest some slowing of the Hubble flow internal to the superclusters. However, the inferred mass densities are low enough to prefer an open universe if the mass-to-luminosity ratios within the best-studied superclusters are comparable to the universal ratio.

A2197 and A2199 are among the nearest rich clusters of galaxies. They are worthy of special attention because (i) they form a close binary system, the analysis of which provides an independent estimate of the clusters' mass to light ratio, and (ii) these two clusters fall along a bridge of interconnected clusters that stretches at least 50 Mpc. We report 78 new redshifts in the A2197+A2199 region, thus tripling the number of known redshifts.

A survey of rich galaxy clusters, redshifts for many of those clusters, and galaxy counts by eye to B = 19.0 show the Indus Supercluster to be an annular (in projection) configuration of nine rich clusters at 0.073 < z < 0.080 apparently connected by bridges of galaxies.

The main structure of the Perseus supercluster is defined by a long chain of clusters and rich groups of galaxies with very similar radial velocities The redshift survey performed by Gregory et al. (1981) has shown that most of the “field” galaxies are also members of the supercluster.

We measured redshifts for a random subsample of 286 objects, m (Shapley) ≤ 16.5, drawn from the catalogue of the Horologium region published by Shapley. The distribution of the sample objects on the celestial sphere is shown in Fig. 1, the characteristics of the redshift distribution are represented in Figs. 2 and 3.

The arguments for “unseen mass”, and the evidence on its distribution, are still somewhat controversial as far as the details are concerned.

The adiabatic theory of galaxy formation in neutrino-dominated universes is reviewed. Collisionless damping leads to a density fluctuation spectrum with a cutoff, the nonlinear evolution of which naturally results in the formation of pancakes, strings and voids.

Massive neutrinos (or photinos) dominating galactic halos may decay into less massive particles by emitting ultraviolet photons. The lifetime for this process can be calculated from particle physics in a model-dependent way. The observed ultraviolet background constrains this lifetime to exceed about 1024 seconds. If the photon energy exceeds 13.6 ev, the existence of HI structures from the galactic plane imposes a similar constraint. The existence of Si IV and C IV in the halos of our own and other galaxies could be due to ∼ 50 ev photons emitted by neutrinos or photinos of rest-mass ∼ 100 ev if their lifetime ∼ 1027 seconds. This lifetime could be in agreement with the theoretical value for 100 ev particles.

It is often claimed that massive neutrinos (v's) can solve the “missing mass” problem, but it is not so clear in the particular case of clusters of galaxies (C.O.G.). Let us assume that the unseen matter is composed by massive v's only. If they are cosmological, the v's should obey Fermi-Dirac statistics with a density of ∼ 100 v/cm3/species. But if “relic,” the v's would be so slow (1) that they cannot exist in this form (because of the previous Jeans instability or because they are trapped in wells generated by baryonic matter). Since the time when the v's decoupled from the primeval mixture (T ∼ 3–1 MeV), the v's can be considered as a “gravitational plasma,” so that violent relaxation occurs in inhomogeneous systems, leading to a Lynden-Bell distribution defined by three parameters: ην (numerical density), Vv (r.m.s. velocity) and the v-mass, mv, all unknown. All three of these parameters are, in fact, necessary to define a state of v-matter.

It is now a widely spread opinion that a ratio of 10:1 between dark and luminous matter exists. Supported by the existence of flat rotation curves at large radii for spirals, this fact reinforces cosmological scenarios with, for instance, massive neutrinos. This content of dark matter is often estimated from the dynamical analysis of clusters of galaxies based essentially on the application of the Virial theorem or the monomassive Emden sphere or deduced from numerical simulations. However, a careful examination shows crucial failures in such approaches1, at least the lack of a mass spectrum and/or of a dynamically influent Intra Cluster Medium. This has been included in simple models1 together with other realistic features such as temperature gradient, isovelocity and/or isothermicity of the gravitational plasma. Our aim is thus to account simultaneously for all the available data concerning both galaxies and ICM; namely, the Nonisothermal Multimass Models1 allow us to fit jointly the numerical density profiles of galaxies, the luminosity function, the velocity dispersion profiles versus magnitude or radius, the luminosity segregation2, the X-ray temperature, luminosity and surface brightness profiles.