EMERGE: Empirical predictions of galaxy merger rates since $z\sim6$

Joseph A. O'Leary; Benjamin P. Moster; Thorsten Naab; Rachel S. Somerville

doi:10.1093/mnras/staa3746

paper

EMERGE: Empirical predictions of galaxy merger rates since $z \sim 6$

arXiv:2001.02687 · doi:10.1093/mnras/staa3746

Abstract

We explore the galaxy-galaxy merger rate with the empirical model for galaxy formation, Emerge. On average, we find that between $2$ per cent and $20$ per cent of massive galaxies ( $lo g_{10} (m_{*} / M_{⊙}) \geq 10.3$ ) will experience a major merger per Gyr. Our model predicts galaxy merger rates that do not scale as a power-law with redshift when selected by descendant stellar mass, and exhibit a clear stellar mass and mass-ratio dependence. Specifically, major mergers are more frequent at high masses and at low redshift. We show mergers are significant for the stellar mass growth of galaxies $lo g_{10} (m_{*} / M_{⊙}) ≳ 11.0$ . For the most massive galaxies major mergers dominate the accreted mass fraction, contributing as much as $90$ per cent of the total accreted stellar mass. We reinforce that these phenomena are a direct result of the stellar-to-halo mass relation, which results in massive galaxies having a higher likelihood of experiencing major mergers than low mass galaxies. Our model produces a galaxy pair fraction consistent with recent observations, exhibiting a form best described by a power-law exponential function. Translating these pair fractions into merger rates results in an inaccurate prediction compared to the model intrinsic values when using published observation timescales. We find the pair fraction can be well mapped to the intrinsic merger rate by adopting an observation timescale that decreases linearly with redshift as $T_{obs} = - 0.36 (1 + z) + 2.39$ [Gyr], assuming all observed pairs merge by $z = 0$ .

arXiv commentMNRAS accepted - 23 pages, 15 figures, 3 tables

EMERGE: Empirical predictions of galaxy merger rates since $z \sim 6$

Abstract

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EMERGE: Empirical predictions of galaxy merger rates since z∼6

Abstract

References in corpus (116)

Cited by in corpus (40)

EMERGE: Empirical predictions of galaxy merger rates since $z \sim 6$