In the southern sky, the Centaurus and Pavo “superclusters”, although lying on opposite sides of the Milky Way, show similar redshifts (V ≃ 4500 km s−1). This author and others have suggested earlier that they may really be portions of a single entity. To investigate this further a redshift survey has been undertaken of the Triangulum Australe-Ara region (15h30m < α < 18h45m, −70° < 6 < −50°) that lies between Centaurus and Pavo, but at very low galactic latitude on the Pavo side of the Milky Way. 75 published redshifts have been supplemented by 56 new redshifts. Selection has favoured E-SO galaxies from the ESO catalogue but the varying extinction has made control difficult.

We have completed a deep wide-field galaxy survey (the APM survey) using the Automatic Plate Measuring machine in Cambridge. The APM survey covers 4400 square degrees in the Southern hemisphere and is designed to be complete to a magnitude limit of bJ = 20.5. A more detailed description may be found elsewhere in these proceedings. We are using this survey to generate a new catalogue of galaxy clusters similar to that of Abell (Abell, G.O., 1958, Astrophys. J. Suppl., 3, 211.). Our cluster cataloge will represent a significant improvement over previous work, since we have detailed information on each individual galaxy including position, size profile and magnitude.

The survey consists of 2 samples : SAMPLE A, 85% complete to B(T) = 14.0 in the region between 10 and 14 Hours in R.A. and between −20 and −50 degrees in DEC., SAMPLE B, complete to B(0) = 14.5 in two regions one between R.A. 13 and 14 hours, DEC between −25 and −33, the other between 11 and 12 hours, DEC from −33 to −27.

The work described here has two main goals:

1. (1) To test the usefulness of Abell clusters for locating voids

   It is well known that Abell clusters are not uniformly distributed in three-dimensional space (e.g. Bahcall and Soneira, 1983). Recently, Batuski and Bums (1985a, b) have suggested that Abell clusters tend to form filamentary structures between which there appear to be large regions (50–200 Mpc across) devoid of bright galaxies. The technique of using Abell clusters as tracers of voids is controversial because the correlation length of Abell clusters is so much larger than the galaxy-galaxy correlation length. However, compared to an all-sky magnitude-limited survey, the technique, if valid, potentially reduces the amount of telescope time required to identify significant voids and map them in redshift space. To investigate this possibility we have undertaken a redshift survey of galaxies in the direction of a nearby and relatively compact candidate void surrounded by a ring of Abell clusters.

2. (2) To identify a void suitable for more extensive study.

   Ultimately we would like to know not only the degree to which voids are empty, but also to what extent those galaxies that may be found within a void differ from those in the surrounding shell. Some theorists (e.g. Dekel and Silk, 1986 and references therein) suggest that as a result of biased galaxy formation, galaxies within a void might be expected to be preferentially younger, fainter, more irregular, more metal-poor and more gas-rich than shell galaxies. The region we selected for study is one which forms part of the Haynes and Giovanelli (1986 and references therein) 21 cm redshift survey. It was chosen, in part, because it is of interest to compare optical results with radio data to determine whether or not the two techniques reveal the same structure.

A new and promising use of galaxy objective-prism spectra as a means of highlighting features in the large scale galaxy distribution has been recently reported by Parker et al. (1987). The technique relies on the property that galaxies with identifiable 4000Å features in low dispersion objective-prism spectra are mostly ellipticals (Cooke, 1980), and that early type galaxies seem to delineate structure and clumpiness in the galaxy distribution (e.g. Giovanelli and Haynes, 1982). The effect is most striking when large numbers of objective-prism galaxy spectra are considered. Figure 1 gives the X-Y plot for 1539 galaxies with 4000Å features to Bj=18.7 in one UKST field out of a manually measured sample of 2903 galaxy prism spectra. Substantial clumpiness is evident. This technique can trace structure in the galaxy distribution across many UKST fields to depths of 400 h−1Mpc.

ESO/SRC-J-Atlas plates (film copies) and film copies of UK-Schmidt objective prism J-plates (dispersion 246nm/mm at Hγ) were scanned with the microdensitometer PDS 2020 GM and reduced automatically with the software package ADAS developed at the Astronomical Institute of Muenster University. In a single field (30 square degrees) near the South Galactic Pole 150 000 objects are found up to the limiting magnitude Stars and galaxies are separated. Algorithms for quasar search among the star-like objects are applied and radial velocities determined from the identified emission lines. Follow-up observations with the ESO 3.6m telescope show fair agreement between the redshifts determined from the objective prism plate and from the slit spectra.

We investigate the two point angular correlation function, ω(θ), of faint galaxy samples obtained from COSMOS machine measurements of 3.9m AAT plates. The area of sky used is the largest yet covered to very faint limits(bj<24 over 2.1 deg2 and rF<22 over 1.4 deg2). The power law slope of ω(θ) is found to be consistent with a value of −0.8 at all depths in both passbands (see fig.1). The amplitudes measured by different authors show a large scatter in the blue passband (see fig.2). If this scatter also appied to the red passband (fig.3) we conclude that although a smaller clustering amplitude in the past is preferred, it is not possible to rule out the stable clustering model, and that models in which the clustering is co-moving may be inconsistent with the data.

This paper announces two results from a catalog of redshifts and fluxes for a flux limited sample of 1000 field galaxies (Loh and Spillar, 1986, Ap. J., 307, L1).

We have considered the sample of groups of galaxies identified by M. J. Geller and J. P. Huchra (1983, Astrophys. J. Suppl. 52, 61), omitting the groups which are part of well-known clusters or those which are probably affected by the presence of interlopers. We have searched for possible morphological segregation among spirals in galaxy groups considering the mean-pairwise distance of the members of the galaxy system and the mean distance of the members from the center of the system. All the distances are normalized to the mean-pairwise distance (MPD) and to the mean distance from the center (CD), respectively, of all the members of the groups considered. We divided the family of the spirals (plus irregulars) into two subfamilies (S′ and S″); we included in S′ the early-type spirals (with morphological type code 0≤T≤2) and in S″ the galaxies of the late morphological types (with T ≥ 3). The median values of the ratios MPD(S′)/MPD, MPD(S″)/MPD, CD(S′)/CD, CD(S″)/CD are 0.86, 1.17, 0.95, 1.08, respectively.

The revelation that galaxies are apparently distributed on two dimensional surfaces that enclose bubble-like voids (de Lapparent et al. 1986, Fairall et al. 1985) has raised considerable interest. We have started an ongoing program to identify and confirm the existence of such structures - as extracted from our redshift database and others. We are concerned to measure how close to sphericity the bubbles fall and, in particular, to see how well their centres can be located.

A detailed investigation of the CrB supercluster of galaxies was initiated. More than 50 new radial velocities were determined. The observations were carried out with the 6-m telescope.

We discuss four samples from the Abell (1958) catalog of clusters of galaxies. Our samples are drawn out from the Abell sample and all clusters have richness 2 and 3. With Ho = 100 km/s/Mpc and qo = +1, we examine the following volumes, defined for both galactic hemispheres:

1. (i) RG 3: b 40° for 0° < 1 360° and b 30° for 90° < 1 240°, distance 300 < R < 750 Mpc, N = 35 clusters, 30 of which with known redshift;

2. (ii) RG 3: b −35° for 15° < 1 232°, 150 < R < 600 Mpc, N = 15 (13);

3. (iii) RG 2: b and 1 as (i), 60 < R < 525 Mpc, N = 110 (55);

4. (iv) RG 2: b and 1 as (ii), 120 < R < 600 Mpc, N = 102(14).

A technique developed by us for searching for superclusters of galaxies (Kalinkov and Kuneva, 1985, 1986) has been applied to the both main catalogs of clusters of galaxies, as well as to some subcatalogs:

1. (i) all Abell (1958) clusters,

2. (ii) rich A-clusters (RG > 0),

3. (iii) very rich A-clusters (RG > 1),

4. (iv) X-ray A-clusters,

5. (v) Zwicky et al. (1961–1968) clusters,

6. (vi) A-clusters, identified in the Zwicky catalog.

Evolution of gravitational systems is currently believed to follow a 3-stage scheme:

1. Stage 1: Subclusters form first ouring violent relaxation

2. Stage 2: Dynamical friction mass segregation

3. Stage 3: contraction of core, expansion of halo

Binggeli (A & A, 107, 338, 1982) showed that neighbouring Abell clusters with pair distances less than 30 to 40 h50−1 Mpc show directional correlation. Binggeli's result is based on structure data of 44 Abell clusters (all with zspectr < 0.1). Binggelli's result was questioned by Struble and Peebles (A.J., 90, 582, 1985). They produce a visual estimate of the direction of cluster elongation for 237 clusters. They did not observe reduced probability for small D large Θ pairs.

We have developed a new statistical method based on maximum likelihood to test for the existence of two subclumps in data of arbitrary dimensionality (Fitchett 1987). The statistic, which is called the Lee function, can be calibrated using Monte Carlo simulations under various null hypotheses.

The Struble & Rood catalogue (Ap. J. Supp, 63, 543) of all measured Abell cluster redshifts is analysed, with corrections for the selection biases. This contains 533 redshifts with |b| ≥ 30°, z ≤ 0.3 compared with 104 in the sample of Bahcall & Soneira (Ap. J.270, 20). Although the catalogue contains biases in angular position (redshifts are preferentially measured in apparent “supercluster” regions) the information on redshift clustering is effectively unbiased since one cannot tell a priori whether pairs of clusters close on the sky are really associated in redshift. Thus the distribution of redshift differences for pairs of given angle & distance classes, f(Δz|θ,D1,D2), is a fair sample of the true distribution. Then by normalising to the “correct” angular correlation function, we obtain the joint distribution f(Δz,θ) and hence ξ(r). In practice, in the estimation of ξ we assign each pair a weight a where where wA is the correlation or cross correlation for the appropriate subset of the whole Abell catalogue. This gives ξ(r) ≈ (r/20 h−1Mpc)−1.8, just slightly smaller than the result of Bahcall & Soneira, but here ξ(r) ≈ 0 for r ≥ 50−1Mpc.

The clustering of the background-contributing X-ray sources is reflected in the excess (i.e., non-Poisson) fluctuations in the X-ray background (XRB). Observational limits on ΔI/I can therefore be used to constrain either the clumpiness of X-ray sources or their contribution to the XRB if their clustering properties are known (see Barcons & Fabian 1987 for details).

The diffuse x-ray background extends from about five to 200 keV. The spectrum is very well fit by a thermal bremsstrahlung emission spectrum characterized by a temperature of about (25–40)(l+z) keV, where z is the redshift at which the emission is produced.

The Intra-Cluster Plasma constitutes an archive of the past history of all clusters and of many groups of galaxies: statistical observations of their X-ray emission will set significant constraints on the dynamical, thermal and chemical events in these cosmic structures. Data on the local X-ray luminosity function N(L, z ≃ 0) were provided by the 1st generation X-ray surveys. HEAO II provided an integral of N(L, z) out to z ≃ 0.4, the counts from a subsample of the MSS (Gioia et al. 1984, Ap.J. 283, 495): these counts result very flat, cf. Fig. 2.