The merger-driven evolution of massive galaxies

TL;DR

This study quantifies the evolution of galaxy merger rates for massive galaxies from redshift 0 to 1.2, showing mergers significantly contribute to the growth of massive red galaxies over cosmic time.

Contribution

It provides the first precise measurement of the merger fraction evolution for mass-selected galaxies up to z=1.2 using large survey data.

Findings

Merger fraction evolves as (1+z)^1.21+/-0.25

Galaxies >1e11 M_sun undergo about 0.5 mergers since z=0.6

Merger rates can explain the growth of massive red sequence galaxies

Abstract

We explore the rate and impact of galaxy mergers on the massive galaxy population using the amplitude of the two-point correlation function on small scales for M > 5e10 M_sun galaxies from the COSMOS and COMBO-17 surveys. Using a pair fraction derived from the Sloan Digital Sky Survey as a low-redshift benchmark, the large survey area at intermediate redshifts allows us to determine the evolution of the close pair fraction with unprecedented accuracy for a mass-selected sample: we find that the fraction of galaxies more massive than 5e10M_sun in pairs separated by less than 30 kpc in 3D space evolves as F(z) = (0.0130+/-0.0019)x(1+z)^1.21+/-0.25 between z = 0 and z = 1.2. Assuming a merger time scale of 0.5 Gyrs, the inferred merger rate is such that galaxies with mass in excess of 1e11 M_sun have undergone, on average, 0.5 (0.7) mergers involving progenitor galaxies both more massive than 5e10 M_sun since z = 0.6 (1.2). We also study the number density evolution of massive red sequence galaxies using published luminosity functions and constraints on the M/L evolution from the fundamental plane. Moreover, we demonstrate that the measured merger rate of massive galaxies is sufficient to explain this observed number density evolution in massive red sequence galaxies since z = 1.