Stephen A. Gregory

The COMA/A1367 Supercluster and Its Environs

The three-dimensional galaxy distribution in the region of space surrounding the two rich clusters Coma and A1367 is analyzed by using a nearly complete redshift sample of 238 galaxies with m, 20 h-l Mpc where there appear to be no galaxies whatever. Since tidal disruption is probably responsible for the isolated component of supercluster galaxies, the observations suggest that all galaxies are (or once were) members of groups or clusters. A number of related topics with more general significance are also discussed. (1) The size-to-separation ratio for foreground groups indicates that the redshift of group formation is z 8 9. (2) There is a general correlation between the volume mass density of a galaxy system and the morphologies of the component galaxies. (3) Finally, we speculate that all clusters of richness class z 2 2 are located in superclusters. Subject headings: galaxies : clusters of galaxies: redshifts

Dwarf galaxies in the Coma cluster

Two catalogues of galaxy morphology for the Coma cluster, one magnitude limited and the other diameter limited, are used to investigate the properties of dwarf galaxies in Coma, the densest of the nearby cluster environments. Both surveys cover an area of 3.97 square degrees. The magnitude limited sample is complete to m b =20.0, and the diameter limited survey is complete to 9 arcsec. The source for the galaxy magnitudes - Godwin et al. [MNRAS, 202, 113 (1983)] - also provides (b−r) galaxy colors for ∼90% of the sample. We discuss the radial distribution of all dwarf galaxies in the Coma cluster after sorting them by morphological type: dwarf irregular, dwarf elliptical, and dwarf spheroidal, and based on these distributions assert that (1) dwarf irregulars are not cluster members, (2) dwarf ellipticals track the distribution of E and S0 galaxies, and (3) the population of dwarf spheroidal galaxies, while tracking the E and S0 population in the cluster, has been destroyed in the cluster core

Observations of the Large Scale Distribution of Galaxies

It has long been assumed that clusters of galaxies merge into a smooth “field” of isolated galaxies. Early estimates put 50% of all galaxies into the field. Using new redshift surveys over large areas we find the real distribution of galaxies to be very different. Nearly all galaxies are in clusters or groups covering a range of at least 1000 in mass and richness.

Redshift studies of large-scale structure. I. The south Coma void region

This paper is the first of a series of Steward Observatory redshift surveys aimed at relatively faint galaxy samples covering small areas of the sky of known importance for large-scale-structure programs. This sample of 92 galaxies includes the region alpha = 12 h 30 min - 13 h 30 min, delta = 18-26 deg, complete for m(p) = 15.7 or less. No additional galaxies are found in the Coma void, and the void is not well described as a bubble. The surveyed supercluster regions appear to have a normal luminosity function. 26 references.

Variability of the broad line spectrum of Markarian 372

We report on spectroscopic observations of the AGN galaxy Mrk 372. In 1986 the spectrum was that of a Seyfert type 1.5 with very broad permitted lines and modestly broadened forbidden lines. In 1990 the spectrum is that of a Seyfert type 1.9. At Hβ the broad line component disappeared leaving only a very weak, narrow line. Observations near Hα, however, do reveal the presence of a broad component

Redshift surveys of emission-line galaxies

The usefulness of employing samples of emission-line galaxies as alternative means of conducting redshift surveys is discussed. Results in the directions of the Bootes and Coma voids show certain differences. In Bootes approximately ten objects have been identified within the void, but the Coma void appears empty at the same luminosities. The Coma void shows little evidence of having a bubble-like structure; it appears more spongelike. There is a large void behind the Coma/A1367 supercluster that is probably related to the Bootes void.

A2197 + A2199 Supercluster Region

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.