Two Distinct Classes of Quiescent Galaxies Revealed by sizes and morphologies at Cosmic Noon in JWST PRIMER and UNCOVER
Abstract
We present a measurement of the low-mass quiescent size-mass relation at 1<z<3 from the JWST PRIMER and UNCOVER treasury surveys. While high-mass end is well studied, the low-mass end has been previously unexplored due to a lack of samples and observing facilities with sufficient spatial resolution. We select a conservative sample of robust low-mass quiescent galaxy candidates using rest-frame UVJ colors and specific star formation rate criteria. We examine galaxies in both rest-frame optical wavelengths (4000<λ<7500 Å, probed by F150W), which provides high spatial resolution, and rest-frame near-infrared (1<λ<2 μm, probed by F444W), which better traces the stellar mass. Sizes are fit in both bands using 2D-Sérsic modeling with GALFIT. With the impressive spatial resolution afforded by JWST, we confirm an unambiguous flattening of the quiescent size-mass relation in rest-frame optical and near-infrared wavelengths at the low-mass end. These low-mass quenched galaxies have exponential-disk-like morphologies compared to the high Sérsic indices measured in their high-mass counterparts. The flattening, as well as the notably steep size growth at higher masses, is potentially evidence for a distinct difference between mass-driven quenching at the massive end and environmentally-driven quenching at the low-mass end. In particular, environmental quenching would leave the structure and size of low-mass galaxies intact, leading to larger sizes than those predicted by extrapolating the massive galaxy size-mass relation. This change with mass in the slope of the quiescent size-mass relation could also indicate a shift from size growth due to star formation (low masses) to size growth via mergers (massive galaxies).
