James Webb Space Telescope Feed Post

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

Paper abstract: 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 z\sim 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 z\sim 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 8.0\times 10^{-6} Mpc^{-3} and 5.4\times 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.