The Observational Distribution of Internal Velocity Dispersions in Nearby Galaxy Clusters
Abstract
We analyze the internal velocity dispersion σ of a sample of 172 nearby galaxy clusters (z <= 0.15), each of which has at least 30 available galaxy redshifts and spans a large richness range. Cluster membership selection is based on nonparametric methods. In the estimate of galaxy velocity dispersion, we consider the effects of possible velocity anisotropies in galaxy orbits, the infall of latetype galaxies, and velocity gradients. The dynamical uncertainties due to the presence of substructures are also taken into account. Previous σ distributions, based on smaller cluster samples, are complete for the Abell richness class R >= 1. In order to improve σ completeness, we enlarge our sample by also including poorer clusters. By resampling 153 AbellAbellCorwinOlowin clusters, according to the richness class frequencies of the EdinburghDurham Cluster Catalog, we obtain a cluster sample which can be taken as representative of the nearby universe. Our cumulative σdistribution agrees with previous distributions within their σ completeness limit (σ ~> 800 km s^1^). We estimate that our distribution is complete for at least σ >= 650 km s^1^. In this completeness range, a fit of the form dN is proportional to σ^{alpha}^dσ gives α = (7.4^+0.7^_0.8_), in fair agreement with results coming from the Xray temperature distributions of nearby clusters. We briefly discuss our results with respect to σ distributions for galaxy groups and to theories of largescale structure formation.
 Publication:

The Astrophysical Journal
 Pub Date:
 December 1996
 DOI:
 10.1086/178180
 arXiv:
 arXiv:astroph/9606098
 Bibcode:
 1996ApJ...473..670F
 Keywords:

 GALAXIES: CLUSTERS: GENERAL;
 GALAXIES: DISTANCES AND REDSHIFTS;
 GALAXIES: KINEMATICS AND DYNAMICS;
 Astrophysics
 EPrint:
 18 pages, latex file with macros included, 9 figures and 6 tables (automatically included), ApJ in press