The virial masses of clusters of galaxies and the effects of contamination

Abstract

Model clusters selected from n-body simulations of clustering are used to evaluate the accuracy of virial methods in mass determination. Clusters having high virial masses due to contamination are identifiable by means of a chi-squared test which compares line-of-sight velocities with a normal distribution. For clusters with good chi-squared fits, the virial mass-to-actual mass ratio obtained indicates that a large degree of scatter inheres in the virial method. Atteention is given to mass-to-light ratio results for the Coma, A2151, and Hercules Supercluster formations. While the last of these is seriously contaminated, solar mass/solar luminosity ratios of 201 and 168 are derived for the other two. These ratios, however, are held to be uncertain by a factor of at least 3, and may therefore be due to 'massive halo' galaxies and intracluster gas.