EMERGE: Empirical predictions of galaxy merger rates since $zsim6$. (arXiv:2001.02687v3 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+OLeary_J/0/1/0/all/0/1">Joseph A. O'Leary</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Moster_B/0/1/0/all/0/1">Benjamin P. Moster</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Naab_T/0/1/0/all/0/1">Thorsten Naab</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Somerville_R/0/1/0/all/0/1">Rachel S. Somerville</a>
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 ($log_{10}(m_{*}/M_{odot}) geq 10.3$) 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
$log_{10}(m_{*}/M_{odot}) gtrsim 11.0$. 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 $T_{mathrm{obs}} = -0.36(1+z)+2.39$ [Gyr],
assuming all observed pairs merge by $z=0$.
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 ($log_{10}(m_{*}/M_{odot}) geq 10.3$) 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
$log_{10}(m_{*}/M_{odot}) gtrsim 11.0$. 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 $T_{mathrm{obs}} = -0.36(1+z)+2.39$ [Gyr],
assuming all observed pairs merge by $z=0$.
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