The merger-driven evolution of massive galaxies

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_* > 5×10¹⁰M_⊙ 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 closepair fraction with unprecedented accuracy for a mass-selected sample: we find that the fraction of galaxies more massive than 5×10 ¹⁰M_⊙ in pairs separated by less than 30 kpc in three-dimensional space evolves as F(z) = (0.0130 ± 0.0019)×(1 + z)^1.21±0.25 between z = 0 and z = 1.2. Assuming a merger timescale of 0.5 Gyr, the inferred merger rate is such that galaxies with mass in excess of 10¹¹M_⊙ have undergone, on average, 0.5 (0.7) mergers involving progenitor galaxies both more massive than 5×10¹⁰M_⊙ 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 theM/L_B evolution from the fundamental plane. Moreover, we demonstrate that themeasured merger rate of massive galaxies is sufficient to explain this observed number density evolution inmassive red sequence galaxies since z = 1.