Assessing the Accuracy of Masses and Spatial Correlations of Galaxy Groups

Abstract

Two algorithms for the identification of galaxy groups from redshift surveys are tested by application to simulated data derived from N-body simulation. The accuracy of the membership assignments by these algorithms is studied in a companion to this paper (Frederic 1994). Here we evaluate the accuracy of group mass estimates and the group-group correlation function. We find a strong bias to low values in the virial mass estimates of groups identified using the algorithm of Nolthenius \& White (1987). The Huchra \& Geller (1982) algorithm gives virial mass estimates which are correct on average. These two algorithms result in group catalogs with similar two-point correlations. We find that groups in a CDM model have excessively large mass to light ratios even when the group richness distribution agrees with observations. We also find that our CDM groups are more strongly correlated than individual halos (galaxies), unlike the groups in the CfA redshift survey extension.