Investigating galaxy size growth and stellar mass assembly through the buildup of stellar haloes since z ∼ 1.1

Abstract

In our current theoretical framework of galaxy formation and evolution, galaxies assemble stellar halo components through galaxy-galaxy interactions and accretion of ex-situ material. Studying this buildup of stellar haloes helps us better understand the processes driving the size growth and mass assembly of galaxies. In this work, we investigate the stellar halo assembly of &sim;500,000 galaxies over 0.2&le; z &le;1.1, by analyzing the evolution in their radial surface brightness and colour profiles. We find that since z=1.1 more massive galaxies assemble larger and brighter stellar haloes, and this assembly is inducing negative colour gradients. Quiescent galaxies grow more through ex-situ accretion than star-forming galaxies of similar masses, which results in faster evolution of quiescent galaxy sizes (<em>R</em>_e). Our results suggest that minor mergers drive the size growth of galaxy haloes since z=1.1, while major mergers fuel the mass assembly and further size growth of the most massive (M_⋆&ge;10^10.5M_⊙) quiescent galaxies.