A Study of Three Groups of Galaxies: Plausible Explanation of the Virial Mass Discrepancy
Abstract
We have made a theoretical and observational study of the de Vaucouleurs groups of galaxies, numbers 6, 12, and 51. With reasonable masstolight ratios (i.e., MIL = 7 for spirals) these groups show large virial mass discrepancies of the order of M th 4OOM1 . We have made 21cm observations which allow us to place upper limits (3 confidence level) on the amount of H I present. For bound cluster models we find M(H 1) < 0.O34MvT, <O.Ol9MvT, <O.O35MvT for groups 6, 12, and 51, respectively. We discuss some of the difficulties of models in which the clusters are bound by intergalactic gas or are unbound due to ejection of gas in the past. A reasonable explanation of the virial mass discrepancies was found, however. It is that the galaxies in these groups are nothing more than ordinary field galaxies that happen to be nearest neighbors of each other. The groups' velocity dispersions are provided by cosmological expansion. Consider a homogeneous expanding universe. Go out a distance D from us and construct a small sphere of radius r . Treating the galaxies within this sphere as constituting a group, one finds MVT = (q0*) 1ML, where q0* = (pi !2p t) is the contribution to the Universe's deceleration parameter made by luminous galaxies. With Shapiro's estimate of q0* 0.005 one predicts MVT 200ML, in reasonable agreement with the observed values. Subject headings: cosmology  galaxies, clusters of
 Publication:

The Astrophysical Journal
 Pub Date:
 December 1973
 DOI:
 10.1086/152544
 Bibcode:
 1973ApJ...186..777G