A Direct Measurement of Galaxy Major and Minor Merger Rates and Stellar Mass Accretion Histories at Z < 3 Using Galaxy Pairs in the REFINE Survey

Abstract We measure the role of major and minor mergers in forming the stellar masses of galaxies over redshifts 0 10 11 M ⊙ selection, we find that over 0 0.84 − 0.2 + 0.3 times on average, while minor mergers down to ratios of 1:10 occur on average 1.43 − 0.3 + 0.5 times per galaxy. We also quantify the role of major and minor mergers in galaxy formation, whereby the increase in mass due to major mergers is 93 − 31 + 49 % while minor mergers account for an increase of 29 − 12 + 17 % using a M * > 10 11 M ⊙ selection. We thus find that major mergers add more stellar mass to galaxies than minor mergers over this epoch. Overall, mergers will more than double the mass of massive galaxies over this epoch when selecting by stellar mass. We however find a lower increase in stellar mass when selecting by a constant number density. Finally, we compare our results to simulations, finding that minor mergers are overpredicted in Illustris and in semi-analytical models, suggesting a mismatch between observations and theory in this fundamental aspect of galaxy assembly.