2008/11/30 by Kyle R. Stewart, James S. Bullock, E. J. Barton +2 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Galaxies: Formation, Evolution, Phenomena #Gamma-ray bursts and supernovae #astro-ph
paper · pdf · doi:10.1088/0004-637x/702/2/1005
published as Astrophys.J.702:1005-1015,2009 · 11 pages, 4 figures, 2 tables; v2 updated to match published version in ApJ. Includes expanded discussion, and fixes typo in "galaxy stellar mass mergers" fitting paramters. Primary results and conclusions unchanged
openalex publication_date 2009/08/18 · arxiv created 2009/11/14 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We employ a high-resolution ΛCDM N -body simulation to present merger rate predictions for dark matter (DM) 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 investigate both rate at which subhalos first enter the virial radius of a larger halo (the "infall rate"), and the rate at which subhalos become destroyed, losing 90% of the mass they had at infall (the "destruction rate"). For both merger rate definitions, we provide a simple "universal" fitting formula that describes our derived merger rates for DM 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 (destruction) 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 ) Gyr −1 (1 + z ) 2.1 . 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 ( t < 100 Myr). This suggests that short-lived, merger-induced bursts of star formation should not contribute significantly to the global star formation rate at early times, in agreement with several observational indications. In contrast, a fairly high fraction (∼20%) of those z = 2 galaxies should have experienced a morphologically transformative merger within a virial dynamical time (∼500 Myr at z = 2). We compare our results to observational merger rate estimates from both morphological indicators and pair-fraction-based determinations between z = 0and2 and show that they are consistent with our predictions. However, we emphasize that great care must be made in these comparisons because the predicted observables depend very sensitively on galaxy luminosity, redshift, overall mass ratio, and uncertain relaxation timescales for merger remnants. We show that the majority of bright galaxies at z = 3 should have undergone a major merger (>0.3) in the previous 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).