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

TL;DR

This study uses JWST observations to analyze 24 massive quiescent galaxies at redshifts 1-3, revealing rapid starburst and quenching episodes, diverse quenching pathways, and potential AGN involvement, shedding light on galaxy evolution during cosmic noon.

Contribution

First detailed JWST-based analysis of star formation histories and quenching mechanisms in massive galaxies at cosmic noon, highlighting rapid quenching following starbursts.

Findings

Massive galaxies experienced large starbursts followed by rapid quenching.

Quenching times range from 0.06 to 1.75 Gyr, indicating multiple pathways.

Evidence of weak AGN activity in some galaxies.

Abstract

We study 24 massive quiescent galaxies with $\log \textrm{M}_*/\textrm{M}_\odot > 10$ 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 ($100\textrm{ M}_{\odot} \textrm{yr}^{-1} -1000 \textrm{ M}_{\odot} \textrm{yr}^{-1}$), 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 $\sim600$ Myr, with more massive galaxies ($\log \textrm{M}_*/\textrm{M}_\odot > 10.7$) 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.