The JWST EXCELS survey: Insights into the nature of quenching at cosmic noon

Abstract

We study 24 massive quiescent galaxies with $\log {\text{M}}_{\ast }/{\text{M}}_{\odot }>10$ at $1<z<3$ with JWST/NIRSpec medium-resolution observations from the Early eXtragalactic Continuum and Emission Line Survey (EXCELS). We reconstruct their star formation histories and find that they have large bursts ($100{\text{ M}}_{\odot }{\text{yr}}^{-1}-1000{\text{ M}}_{\odot }{\text{yr}}^{-1}$), followed by a rapid truncation of star formation. The number densities of the quenched galaxies in our sample that we predict underwent a submillimeter phase are consistent with submillimeter galaxies being the progenitors of our quenched population. The median post-starburst visibility time is $\sim 600$ Myr, with more massive galaxies ($\log {\text{M}}_{\ast }/{\text{M}}_{\odot }>10.7$) exhibiting shorter visibility times than lower mass galaxies. The range of quenching times -- defined as the time from the peak starburst to the time of quiescence -- found in this sample ($0.06-1.75$ Gyr) suggests multiple quenching pathways, consistent with previous studies. We do not see evidence for quenching mechanisms varying with redshift between $1<z<3$. We detect evidence for weak AGN activity in 4 out of the 8 galaxies with robust emission line detections, based on line ratio diagnostics. Our findings suggest that there are a diverse range of quenching mechanisms at cosmic noon, and support a scenario in which the primary quenching mechanisms are rapid ($<500$ Myr) following a starburst.

Accepted for publication in The Astrophysical Journal