Nearby groups of galaxy clusters.
Abstract
The spatial distribution of 27 Abell clusters in distance classes 02 and the surface distribution of 249 Abell clusters in distance classes 34 are examined for evidence of spatial grouping. Groups with mean cluster number densities two or more orders of magnitude greater than that of the surrounding field are identified by applying quantitative nearestneighbor statistical criteria to the cluster distributions. In this way, five definite groups in distance classes 02 and 39 probable groups in distance classes 34 are identified which contain clusters separated from one another by less than 25 Mpc. It is found that about 40% of the nearby Abell clusters occur in groups, that binary and triplet clusters are more numerous than groups with four or more members, and that the BautzMorgan types of clusters within the groups tend to differ from the types outside them. The radial and tangential components of the separation vectors of clusters in nearby groups are shown to have values that are consistent with the hypothesis that cluster redshift differences are caused by the cosmological expansion of the Universe.
 Publication:

The Astrophysical Journal
 Pub Date:
 July 1976
 DOI:
 10.1086/154461
 Bibcode:
 1976ApJ...207...16R
 Keywords:

 Astronomical Catalogs;
 Galactic Clusters;
 Red Shift;
 Spatial Distribution;
 Statistical Analysis;
 Frequency Distribution;
 Probability Distribution Functions;
 Tables (Data);
 Astrophysics