The Growth of Galaxy Stellar Haloes over 0.2 ≤ z ≤ 1.1

Galaxies are predicted to assemble their stellar haloes through the accretion of stellar material from interactions with their cosmic environment. Observations that trace stellar halo buildup probe the processes that drive galaxy size and stellar mass growth. We investigate stellar halo assembly over 0.2 ≤ z ≤ 1.1 in a mass-complete ( M _⋆ ≥ 10 ^9.5 M _⊙ ) sample of 242,456 star-forming galaxies (SFGs) and 88,421 quiescent galaxies (QGs) from the CLAUDS and HSC-SSP surveys. We extract galaxy rest-frame g -band surface brightness ( μ _g ) profiles to study faint, extended emission in galaxy outskirts. We examine trends in galaxy assembly by analyzing the median μ _g profiles in different SFG and QG M _⋆ ranges with decreasing redshift and connecting evolution in galaxy μ _g profiles with the underlying stellar mass growth in galaxies. Since z = 1.1, the majority of evolution in the median μ _g profiles of galaxies (∼64% in SFGs and ∼71% in QGs) occurs throughout their stellar halo regions (2–10 R _e ). More-massive galaxies assemble stellar halo material more rapidly at 0.2 ≤ z ≤ 1.1. Over this period, QGs grow a larger fraction of their stellar haloes than SFGs at fixed M _⋆ (factor of ∼1.2). Although star formation can account for the stellar halo growth observed in low-mass SFGs (10 ^9.5 M _⊙ ≤ M _⋆  < 10 ^10.5 M _⊙ ), high-mass SFGs ( M _⋆ ≥ 10 ^10.5 M _⊙ ), and both low- and high-mass QGs require an additional assembly mechanism. Our results suggest accretion via minor mergers drives additional stellar halo growth in these galaxies. The contribution from accretion is larger in more-massive galaxies (over M _⋆ ≥ 10 ^9.5 M _⊙ ), and QGs exhibit larger fractional increases to their ex situ fractions over 0.2 ≤ z ≤ 1.1 than SFGs at fixed M _⋆ .