The Growth of Galaxy Stellar Haloes Over $0.2 \leq z \leq 1.1$

TL;DR

This study investigates how galaxy stellar haloes grow from redshift 1.1 to 0.2, revealing that accretion and minor mergers significantly contribute to halo assembly, especially in more massive and quiescent galaxies.

Contribution

It provides new observational evidence on the evolution of stellar haloes across a wide redshift range, highlighting the role of accretion and mergers in galaxy growth.

Findings

Majority of halo evolution occurs between 2-10 R_e.

More massive galaxies assemble halos faster.

Quiescent galaxies grow larger halo fractions than star-forming ones.

Abstract

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 $0.2 \leq z \leq 1.1$ in a mass-complete ($M_{\star} \geq 10^{9.5}M_{\odot}$) sample of 242,456 star-forming and 88,421 quiescent galaxies (SFGs and QGs) from the CLAUDS and HSC-SSP surveys. We extract galaxy rest-frame $g$-band surface brightness ($\mu_g$) profiles to study faint, extended emission in galaxy outskirts. We examine trends in galaxy assembly by analyzing the median $\mu_g$ profiles in different SFG and QG \msS ranges with decreasing redshift and connecting evolution in galaxy $\mu_g$ profiles with the underlying stellar mass growth in galaxies. Since $z=1.1$, the majority of evolution in the median $\mu_g$ profiles of galaxies ($\sim$64$\%$ in SFGs and $\sim$71$\%$ in QGs) occurs throughout their stellar halo regions (2-10$R_e$). More massive galaxies assemble stellar halo material more rapidly at $0.2 \leq z \leq 1.1$. Over this period, QGs grow a larger fraction of their stellar haloes than SFGs at fixed $M_{\star}$ (factor of $\sim$1.2). Although star formation can account for the stellar halo growth observed in low-mass SFGs ($10^{9.5}M_\odot \leq M_\star < 10^{10.5}M_\odot$), high-mass SFGs ($M_\star \geq 10^{10.5}M_\odot$) 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 $M_{\star} \geq 10^{9.5}M_{\odot}$), and QGs exhibit larger fractional increases to their ex-situ fractions over $0.2 \leq z \leq 1.1$ than SFGs at fixed $M_{\star}$.