VELOCITY DISPERSIONS IN GALAXY CLUSTERS

We analyze the velocity dispersions of 79 galaxy clusters having at least 30 galaxies with available redshifts. We show that different estimates of velocity dispersion give similar results on cluster samples of at least approximately 20 galaxies each. However, only robust estimates of velocity dispersion seem to be efficient on cluster samples with approximately 10 galaxies each. A significant correlation is found to exist between the velocity dispersion and the cluster richness. We provide the distribution function of cluster velocity dispersions, normalized to the complete sample by Abell, Corwin, & Olowin (1989). Available theoretical models are compared with this distribution function.