Minor vs Major Mergers: The Stellar Mass Growth of Massive Galaxies from z=3 using Number Density Selection Techniques

TL;DR

This study investigates the stellar mass growth of massive galaxy progenitors from redshift 3 to 0.3, highlighting the roles of star formation, mergers, and external mass accretion using number density selection techniques.

Contribution

It introduces a method to track galaxy progenitors considering major mergers, providing new insights into their mass growth and size evolution over cosmic time.

Findings

Massive galaxy progenitors grow by a factor of four in stellar mass from z=3 to 0.3.

Approximately 51% of the stellar mass at z=0.3 is acquired externally since z=3.

Average cold gas accretion rate is about 66 solar masses per year between z=1.5 and z=3.

Abstract

We present a study on the stellar mass growth of the progenitors of local massive galaxies with a variety of number density selections with $n\le1\times10^{-4}\,\rm{Mpc^{-3}}$ (corresponding to $M_*=10^{11.24}\rm{M_{\odot}}$ at z=0.3) in the redshift range $0.3<z<3.0$. We select the progenitors of massive galaxies using a constant number density selection, and one which is adjusted to account for major mergers. We find that the progenitors of massive galaxies grow by a factor of four in total stellar mass over this redshift range. On average the stellar mass added via the processes of star formation, major and minor mergers account for $24\pm8\%$, $17\pm15\%$ and $34\pm14\%$, respectively, of the total galaxy stellar mass at $z=0.3$. Therefore $51\pm20\%$ of the total stellar mass in massive galaxies at $z=0.3$ is created externally to their z=3 progenitors. We explore the implication of these results on the cold gas accretion rate and size evolution of the progenitors of most massive galaxies over the same redshift range. We find an average gas accretion rate of $\sim66\pm32\,\rm{M_{\odot}yr^{-1}}$ over the redshift range of $1.5<z<3.0$. We find that the size evolution of a galaxy sample selected this way is on average lower than the findings of other investigations.