This session on the cosmic background radiation is remarkable for the quality of the interesting new results presented and the controversy over substantive issues. This paper reviews the status of measurements of the spectrum and anisotropy of the cosmic background and summarizes what is known of the properties of the cosmic background radiation: its spectrum, anisotropy, polarization, and statistics.

The effort to measure the geometry of space by experiment, that is, the determination of the Hubble Constant, Ho, and of the deceleration parameter, qo, led toward the end of the first half of the century, to the classical paper by Humason, Mayall, and Sandage (1956). Their catalogue contains 920 redshifts collected over a twenty-year period (1935–1955). Further redshifts of galaxies were measured to refine such determinations and to study the dynamics of clusters (Zwicky 1933).

We have completed the survey of radial velocities for all 2400 galaxies brighter than 14.5 at high galactic latitude in the northern hemisphere. This data set has already been used to derive a good measure of the local mean mass density, describe the overdensity and the dynamics of the local supercluster and to analyse the dynamics of groups and clusters of galaxies within the sample volume.

The aim of the survey is to sample a relatively large, randomly chosen volume of the Universe in order to study the large-scale distribution of galaxies using the two-point correlation function, the peculiar velocities between galaxy pairs and to provide an estimate of the galaxian luminosity function that is unaffected by density inhomogeneities and Virgo infall.

A catalogue of radial velocities of galaxies has been completed which lists all radial velocities published until the end of December, 1980, for galaxies in both the northern and the southern hemispheres.

For each galaxy the catalogue provides R.A. and Declination, name(s) of the galaxy (NGC, IC, 3 CR, etc.), each known heliocentric radial velocity with its reference, and the type of observation (whether optical or radio).

We are searching for clusters of galaxies on photographs taken for the Southern Sky Survey with the U.K. Schmidt telescope at Siding Spring, and we are preparing a comprehensive catalogue of the southern clusters. The purpose is to extend the early cluster survey made from the Palomar Sky Survey (Abell 1958) to full-sky coverage. We are taking special pains to delineate those clusters in the new southern survey that as nearly as possible match those criteria set for the northern survey clusters to be included in a homogeneous statistical sample. It is our expectation, therefore, that there will be a homogeneous all-sky sample of clusters for studying the large-scale distribution of matter in the universe.

An attempt is made to establish the membership of Abell clusters in superclusters of galaxies. The relation

is used to calibrate the distances to the clusters of galaxies with two redshift estimates. One is m10, the magnitude of the ten-ranked galaxy, and the other is the “mean population,” P, defined by:

where p = 40, 65, 105 … galaxies for richness groups 0, 1, 2 …, and r is the apparent radius in degrees given by:

The first iteration for redshift, z1, is obtained from m10 alone:

The standard deviation for Eq. (1) is 0.105, the number of clusters with known velocities is 342 and the correlation coefficient between observed and fitted values is 0.921. With zi from Eq. (1), we define Cartesian galactic coordinates Xi = Rih−1 cosBi cosLi, Yi = Rih−1 cosBi sinLi, Zi = Rih−1 sinBi for each Abell cluster, i = 1, …, 2712, where Ri is the distance to the cluster (Mpc), and Ho = 100 h km s−1 Mpc−1.

A new processing of the surface distribution of clusters from the catalogues of Abell and Zwicky has been carried out for an area of 2000 square degrees around the NGP. Four statistical tests (M. Kalinkov, I. Kuneva, 1980, C.R. Acad. Bulg. Sci., 33, 1305) are applied to search apparent characteristic sizes. Assuming a mean distance R = 440 h−1 Mpc (Ho = 100 h km s−1 Mpc−1) to Abell clusters, a characteristic size Q = 52 Mpc for superclusters has been obtained. For Distance Group 5 (R = 400 Mpc) and for Distrance Group 6 (R = 530 Mpc), we have Q = 48 Mpc and Q = 40 Mpc, respectively. For Zwicky D clusters (R = 390 Mpc, assuming a uniform distribution in the volume from 300 to 450 Mpc, Q = 55 Mpc and for ED clusters R ≈ 650 Mpc), Q = 46 Mpc. Therefore, the mean characteristic size of superclusters is 50 h−1 Mpc. There is an exception, however, for VD clusters (R = 540 Mpc) for which Q ≈ 100 h−1 Mpc.

The topic of quasars and superclusters is only a few years old. Although the first pairs of quasars with small angular separations on the sky were found ten years ago (Stockton 1972, Wampler et al. 1973), the pair members had very different redshifts. The surface density of samples with available redshifts at that time was far too low for cases of quasars with both small angular separations and small redshift differences to turn up. Setti and Woltjer (1977) pointed out that if quasars occur in the nuclei of giant elliptical galaxies, then clustering should be apparent at 20th magnitude and fainter. In 1979 Walsh, Carswell and Weymann found a very close pair with identical redshifts; that, of course, was the first discovery of a gravitational lens. Also in 1979 Arp, Sulentic, and di Tullio showed that some of the quasars near NGC 3389 had similar redshifts, although at that time they did not discuss the hypothesis of the quasars being associated with superclusters. Subsequently Burbidge et al. (1980) confirmed that a compact (5 minutes of arc) group of 3 quasars found by Hoag on a 4m grating prism plate of the M82 field had very similar redshifts. Indeed, the group had the dimensions of a galaxy cluster, not a supercluster. Oort, Arp, and de Ruiter (1981) then specifically called attention to the fact that enough pairs of quasars with similar redshifts were known to suggest that quasar associations on the scale of galaxy superclusters do exist.

We analyze the different contributing factors in a previous study by Seldner and Peebles (1979) who found statistically significant evidence for a correlation between a list of 382 QSOs at |b| > 40°, δ > −23° and the Lick counts of galaxies (m < 19.0), namely, that there are on the average 1.45 ± 0.39 more galaxies within 15′ of a QSO than expected if QSOs were placed at random across the sky. Taking into account these different factors and using a larger sample of QSOs whose detection is not expected to bias our statistical results, we conclude that: i) There is no longer statistically significant evidence for an excess of Lick galaxies close to QSOs from our list considered as a whole. After removing the different possible biases, if there was any excess left in that previous study, it was rather due to radio QSOs and not to optical QSOs. This effect is marginal if we adopt a mean density of galaxies in a ring between 2° and 5°, and null if the mean density is taken between 1° and 2° from QSOs; ii) The whole correlation function w(θ) shows in general a hump between and 2°. This is either an off-set value or a maximum value preceding a slow decrease in w(θ) between and 5°. This feature seems to pertain more to high redshift QSOs (z > 0.4) and to radio QSOs than to optical QSOs. It seems slightly more pronounced at the polar galactic caps and at very low galactic latitudes; iii) Numerical simulations seem to indicate that the error bars determined by assuming that cell numbers are independent are slightly underestimated. They reproduce fairly well some features within 1° from the QSOs and suggest that the hump at would not be as unlikely as indicated by the error bars.

Radial velocities have been measured for 231 galaxies chosen by apparent magnitude from 282 small fields spanning the area on the sky thought to contain the Bootes void. The galaxy distribution exhibits a spherical volume 6000 km/s in diameter in which no objects are found. The rms velocity difference of close pairs in our sample is less than 180 km/s.

In the past few years the large scale structure and dynamics of the galaxy distributions have been studied intensively, mainly by means of red-shift surveys. From these surveys it seems that the distribution of galaxies is characterised by large, empty voids of (20–40) h−1100 Mpc in diameter with a typical density contrast of δ ∼ - (0.7–0.8).

Isolated galaxies seem to have more nuclear activity and less disk activity than nonisolated objects. This is interpreted as an expression of the mass-profile in their halos.

The discovery of voids in the three-dimensional distribution of galaxies has rapidly been followed by claims that in at least one such void some objects, like Markarian and emission-line galaxies, are present. Why are only active galaxies found in these voids? Should we also expect the opposite to be true, namely that active galaxies ought to be found more often in voids, or in regions of the Universe with lower-than-average density? There are indications that this seems to be the case, as Gisler (1978) found that emission-line galaxies, Markarians and possibly Seyferts avoid environments of dense clusters. Differences between “field” and “cluster” populations are probably due more to the enhanced local density of galaxies than to the nature of the overall environment.

I want to “make propaganda” for some calculations carried out at Cornell; a detailed paper is available on this work (Hoffman, Salpeter and Wasserman 1982, hereafter HSW), so I only summarize it briefly (Sect. 2) and concentrate mainly on implications. Like previous work by Peebles (1982) and by Occhionero et al (1982), these calculations use spherically symmetric models without dissipation for the dynamical development of large voids and galaxy clusters (and superclusters) from small underdensities and overdensities, respectively, at the recombination era. We now know how this development depends on various parameters and on the asymmetries between over- and under-densities. I discuss conjectures for more complex geometries in Sect. 3.

We present a unified algorithm which describes the non-linear growth 1) of condensations surrounded by cavities or 2) of cavities surrounded by condensations (i.e. ridges of higher density) in the Hubble flow. The main idealization is that of pressureless spherical symmetry (Tolman-Bondi solution); overall algebraic details and results for problem 1) are given in previous work (Occhionero, et al., 1981 a and b); results for problem 2) will be given elsewhere (Occhionero, et al., 1982).

The isothermal theories of galaxy formation encounter serious difficulties in accounting for the existence of large voids (see, e.g., Aarseth and Saslow 1982). The alternative picture of adiabatic fluctuations and pancake collapse (see, e.g., Doroshkevich et al. 1978 and references therein) faces difficulties due to: i) observed correlation functions, and ii) the absence of small-scale fluctuations in the microwave background.

About 500 remote, mainly compact clusters of galaxies have been identified on ESO (R) Schmidt plates; around 40 of these have been observed with the ESO CCD camera on the Danish 1.5-m telescope on La Silla. We describe the method of identifying the clusters and give some preliminary photometric results.

Cosmology can mean many different things to different people. Sandage (1970) once described it as “the search for two numbers” (Ho and qo). At the other end of the spectrum, it may comprise almost all the interesting bits of astronomy and physics that bear on how the universe got to be the way it is. Supernovae can probe many of these bits because they are bright, have been going on for a long time, and contribute directly to the chemical and, perhaps, dynamical evolution of structure in the universe.

Rich galaxy clusters containing multiple condensations are common. This subclustering affects many cluster properties and provides insight into cluster evolution.

“Clumpy” clusters of galaxies are interesting, in part, because N-body simulations indicate that multi-component substructure occurs before complete collapse and virialization (White 1976). Interesting systems can be identified both from x-ray surface brightness maps (Forman et al. 1981) and from contour maps based on galaxy counts (Geller and Beers 1982).

I would like to make a brief comment on some work that John Moody, Edwin Turner and I have done on filamentary structure in the Shane-Wirtanen galaxy counts. The picture of the Shane-Wirtanen galaxy counts to the 19th magnitude appears quite filamentary to the eye. The existence of such filaments is quite important theoretically, since filaments could easily be Zeldovich pancakes seen edge-on, and filamentary structure is expected in general when the perturbation spectrum is cut off at small scales. So if the filaments are real, they are telling us something quite important about the universe. The experience of the Martian “canals” reminds us, however, that the eye is very good at picking linear features in random data, and here we are dealing with a clumpy distribution where such effects may be enhanced.