James Webb Space Telescope Feed Post

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

: Model forcepho photometry, illustrating the data (top row), the Sérsic model (bottom row) and their difference (middle row). The residuals show no clear evidence for a second component, except for F200W, where there is an extended feature which we already noted in Fig. 1a; note how this feature is not present in the other bands, as discussed in § 3. The images are cut along the native pixel grid of the NIRCam detectors; forcepho fits the individual exposures to avoid the correlated uncertainties due to resampling. We report the discovery of a quiescent galaxy at z=2.34 with a stellar mass of only M?=9.5+1.8-1.2×108M?, 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 Gyr with a mass-weighted average stellar age of 0.8-1.7 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-s 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?=8-17×1010M?). 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 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.