Kavli Affiliate: John D. Silverman
| First 5 Authors: , , , ,
| Summary:
At fixed galaxy stellar mass, there is a clear observational connection
between structural asymmetry and offset from the star forming main sequence,
$Delta$SFMS. Herein, we use the TNG50 simulation to investigate the relative
roles of major mergers (stellar mass ratios $mugeq0.25$), minor ($0.1 leq
mu < 0.25$), and mini mergers ($0.01 leq mu < 0.1$) in driving this
connection amongst star forming galaxies (SFGs). We use dust radiative transfer
post-processing with SKIRT to make a large, public collection of synthetic
Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) images of simulated TNG
galaxies over $0.1leq z leq 0.7$ with $log M_{star} /
mathrm{M}_{odot}geq9$ ($sim750$k images). Using their instantaneous SFRs,
known merger histories/forecasts, and HSC-SSP asymmetries, we show (1) that
TNG50 SFGs qualitatively reproduce the observed trend between $Delta$SFMS and
asymmetry and (2) a strikingly similar trend emerges between $Delta$SFMS and
the time-to-coalescence for mini mergers. Controlling for redshift, stellar
mass, environment, and gas fraction, we show that individual mini merger events
yield small enhancements in SFRs and asymmetries that are sustained on long
timescales (at least $sim3$ Gyr after coalescence, on average) — in contrast
to major/minor merger remnants which peak at much greater amplitudes but are
consistent with controls only $sim1$ Gyr after coalescence. Integrating the
boosts in SFRs and asymmetries driven by $mugeq0.01$ mergers since $z=0.7$ in
TNG50 SFGs, we show that mini mergers are responsible for (i) $55$ per cent of
all merger-driven star formation and (ii) $70$ per cent of merger-driven
asymmetric structure. Due to their relative frequency and prolonged boost
timescales, mini mergers dominate over their minor and major counterparts in
driving star formation and asymmetry in SFGs.
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