Merger Rates in Simulated and Observed Groups of Galaxies

Abstract

The occurrence of mergers in simulated loose groups of galaxies (Barnes 1985; Mamon 1987) has generated the concern that mergers may be significantly more frequent in simulated groups than in observed groups (Ostriker 1987). I compare here quantitatively the rates of merging between a subset of 102 groups (Mamon 1986) of the CfA group catalog (Geller and Huchra 1983) and samples of 50 dynamically simulated groups of given initial density. The simulated groups start out virialized with galaxy luminosities pseudo-randomly generated from a Schechter function of index −1 and cutoff 0.5 L* (giving an average luminosity ∼ L*, close to the average in the CfA group catalog). The groups are evolved with the N-body code described in Mamon (1987). The merging time of the sample of 50 simulated groups is defined as the time at which the Tremaine-Richstone (1977) statistic T1 = σ(M1)/〈ΔM12〉 becomes smaller than 0.8. This value of T1 is significantly smaller than expected from a random realization of groups with the luminosity function given above (Mamon 1987).