JADES: deep spectroscopy of a low-mass galaxy at redshift 2.3 quenched by environment

We report the discovery of a quiescent galaxy at $z = 2.34$ with a stellar mass of only $M_{\ast} = 9.5_{-1.2}^{+1.8} \times 10^{8}\ M_{\odot}$ , based on deep JWST/NIRSpec spectroscopy. This is the least massive quiescent galaxy found so far at high redshift. We use a Bayesian approach to model the spectrum and photometry, and find the target to have been quiescent for $0.6\ \mathrm{Gyr}$ with a mass-weighted average stellar age of $0.8-1.7\ \mathrm{Gyr}$ (dominated by systematics). The galaxy displays an inverse colour gradient with radius, consistent with environment-driven quenching. Based on a combination of spectroscopic and robust (medium- and broad-band) photometric redshifts, we identify a galaxy overdensity near the location of the target ($5\sigma$ above the background level at this redshift). We stress that had we been specifically targetting galaxies within overdensities, the main target would not have been selected on photometry alone; therefore, environment studies based on photometric redshifts are biased against low-mass quiescent galaxies. The overdensity contains three spectroscopically confirmed, massive, old galaxies ($M_{\ast} = 8-17 \times 10^{10} M_{\odot}$ ). The presence of these evolved systems points to accelerated galaxy evolution in overdensities at redshifts $z > 2$ , in agreement with previous works. In projection, our target lies only $35\ \mathrm{pkpc}$ away from the most massive galaxy in this overdensity (spectroscopic redshift $z = 2.349$ ) which is located close to overdensity’s centre. This suggests the low-mass galaxy was quenched by environment, making it possibly the earliest evidence for environment-driven quenching to date.

eprint arXiv:2307.08633