Galaxy Mergers and Dark Matter Halo Mergers in Λcdm: Mass, Redshift, and Mass-Ratio Dependence

We employ a high-resolution LCDM N-body simulation to present merger rate predictions for dark matter halos and investigate how common merger-related observables for galaxies--such as close pair counts, starburst counts, and the morphologically disturbed fraction--likely scale with luminosity, stellar mass, merger mass ratio, and redshift from z=0 to z=4. We provide a simple 'universal' fitting formula that describes our derived merger rates for dark matter halos a function of dark halo mass, merger mass ratio, and redshift, and go on to predict galaxy merger rates using number density-matching to associate halos with galaxies. For example, we find that the instantaneous merger rate of m/M>0. 3 mass ratio events into typical L > f L* galaxies follows the simple relation dN/dt=0. 03 (1+f) (1+z) ². 1 Gyr^-1. Despite the rapid increase in merger rate with redshift, only a small fraction of >0. 4 L* high-redshift galaxies (~3% at z=2) should have experienced a major merger (m/M >0. 3) in the very recent past (t0. 3) in the last 700 Myr and conclude that mergers almost certainly play an important role in delivering baryons and influencing the kinematic properties of Lyman Break Galaxies (LBGs). (abridged)