THE GREATER IMPACT OF MERGERS ON THE GROWTH OF MASSIVE GALAXIES: IMPLICATIONS FOR MASS ASSEMBLY AND EVOLUTION SINCEz≃ 1

Using deep infrared observations conducted with the MOIRCS imager on the Subaru Telescope in the northern GOODS field combined with public surveys in GOODS-S, we investigate the dependence on stellar mass, M_*, and galaxy type of the close pair fraction (5 h^ (–1) kpc 10^ (11) M_☉ are more likely to host merging companions than less massive systems (M_* ~ 10^ (10) M_☉). We find evidence for a higher pair fraction for red, spheroidal hosts compared to blue, late-type systems, in line with expectations based on clustering at small scales. The so-called "dry" mergers between early-type galaxies devoid of star formation (SF) represent nearly 50% of close pairs with M_*>3 × 10^ (10) M_☉ at z ~ 0. 5, but less than 30% at z ~ 1. This result can be explained by the increasing abundance of red, early-type galaxies at these masses. We compare the volumetric merger rate of galaxies with different masses to mass-dependent trends in galaxy evolution. Our results reaffirm the conclusion of Bundy et al. that major mergers do not fully account for the formation of spheroidal galaxies since z ~ 1. In terms of mass assembly, major mergers contribute little to galaxy growth below M_* ~ 3 × 10^ (10) M_☉ but play a more significant role among galaxies with M_*≳ 10^ (11) M_☉ ~ 30% of which have undergone mostly dry mergers over the observed redshift range. Overall, the relatively rapid and recent coalescence of high-mass galaxies mirrors the expected hierarchical growth of halos and is consistent with recent model predictions, even if the top-down suppression of SF and morphological evolution (i. e. , "downsizing") involves additional physical processes.