New Techniques for Relating Dynamically Close Galaxy Pairs to Merger and Accretion Rates: Application to the Second Southern Sky Redshift Survey

Abstract

We introduce two new pair statistics, which relate close galaxy pairs to the\nmerger and accretion rates. We demonstrate the importance of correcting these\n(and other) pair statistics for selection effects related to sample depth and\ncompleteness. In particular, we highlight the severe bias that can result from\nthe use of a flux-limited survey. The first statistic, denoted N_c, gives the\nnumber of companions per galaxy, within a specified range in absolute\nmagnitude. N_c is directly related to the galaxy merger rate. The second\nstatistic, called L_c, gives the total luminosity in companions, per galaxy.\nThis quantity can be used to investigate the mass accretion rate. Both N_c and\nL_c are related to the galaxy correlation function and luminosity function in a\nstraightforward manner. We outline techniques which account for various\nselection effects, and demonstrate the success of this approach using Monte\nCarlo simulations. If one assumes that clustering is independent of luminosity\n(which is appropriate for reasonable ranges in luminosity), then these\nstatistics may be applied to flux-limited surveys.\n These techniques are applied to a sample of 5426 galaxies in the SSRS2\nredshift survey. Using close dynamical pairs, we find N_c(-21<M_B<-18) =\n0.0226+/-0.0052 and L_c(-21<M_B<-18) = 0.0216+/-0.0055 10^{10} h^2 L_sun at\nz=0.015. These are the first secure estimates of low-z close pair statistics.\nIf N_c remains fixed with redshift, simple assumptions imply that ~ 6.6% of\npresent day galaxies with -21<M_B<-18 have undergone mergers since z=1. When\napplied to redshift surveys of more distant galaxies, these techniques will\nyield the first robust estimates of evolution in the galaxy merger and\naccretion rates. [Abridged]\n