Mini-Quenching of High-Redshift Galaxies by Bursty Star Formation

Kavli Affiliate: George Efstathiou

| First 5 Authors: Tibor Dome, Sandro Tacchella, Anastasia Fialkov, Avishai Dekel, Omri Ginzburg

| Summary:

The recent observation of a low-mass $z=5.2$ and an intermediate-mass $z=7.3$
(JADES-GS-z7-01-QU) quenched galaxy with JWST / NIRSpec is the first evidence
of halted star formation above $zsim 5$. Here we show how bursty star
formation at high redshift gives rise to temporarily quenched, or miniquenched
galaxies in the mass range $M_{star} = 10^7-10^9 M_{odot}$ using three
models of galaxy formation: the periodic box simulation IllustrisTNG, the
zoom-in simulation VELA and an empirical halo model. The main causes for
mini-quenching are stellar feedback, lack of gas accretion onto galaxies and
galaxy-galaxy interactions. The abundance of mini-quenching events agrees
across the three models: the population first appears below $zsim 8$, after
which the fraction of miniquenched galaxies increases with cosmic time, from
$sim 0.5$% at $z=7$ to $sim 1-2$% at $z=4$, corresponding to comoving number
densities of $8.0times 10^{-6}$ Mpc$^{-3}$ and $5.4times 10^{-4}$ Mpc$^{-3}$,
respectively. The star formation rate duty cycle ($f_{mathrm{duty}}sim
99.56^{+0.4}_{-4.5}$% at $z=7$) inferred for VELA galaxies is consistent
therewith. Star formation histories (SFHs) in VELA suggest that mini-quenching
at $z=4-8$ is short-lived with a duration of $sim 20-40$ Myr, which is close
to the free-fall timescale of the inner halo. However, mock spectral energy
distributions of miniquenched galaxies in IllustrisTNG and VELA do not match
JADES-GS-z7-01-QU photometry, unless their SFHs are artificially altered to be
more bursty on timescales of $sim 40$ Myr. Studying miniquenched galaxies
might aid in calibrating the sub-grid models governing galaxy formation, as
these may not generate sufficient burstiness at high redshift to explain the
SFH inferred for JADES-GS-z7-01-QU.

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