<i>JWST</i> PRIMER: strong evidence for the environmental quenching of low-mass galaxies out to <i>z</i>≃ 2

ABSTRACT We present the results of a study investigating the galaxy stellar-mass function (GSMF), size–mass relations, and morphological properties of star-forming and quiescent galaxies over the redshift range $0.25 &amp;lt; z &amp;lt; 2.25$, using the JWST PRIMER survey. The depth of the PRIMER near-IR imaging allows us to confirm the double Schechter function shape of the quiescent GSMF out to $z \simeq 2.0$, via a clear detection of the upturn at $\mathrm{log}_{10} (M_{\star }/\mathrm{M}_{\odot })\le 10$ thought to be induced by environmental quenching. Additionally, we confirm that quiescent galaxies can be split into separate populations at $\mathrm{log}_{10} (M_{\star }/\mathrm{M}_{\odot })\simeq 10$, based on their size–mass relations and morphologies. We find that low-mass quiescent galaxies have more disc-like morphologies (based on Sérsic index, Gini coefficient, and $M_{20}$ metrics) and follow a shallower size–mass relation than their high-mass counterparts. Indeed, the slope of the size–mass relation followed by low-mass quiescent galaxies is indistinguishable from that followed by star-forming galaxies, albeit with a lower normalization. Moreover, within the errors, the evolution in the median size of low-mass quiescent galaxies ($R_\mathrm{{e}} \propto (1+z)^{-0.22\pm 0.10})$ is indistinguishable from that followed by star-forming galaxies, and significantly less rapid than that displayed by high-mass quiescent galaxies ($R_\mathrm{{e}} \propto (1+z)^{-1.48\pm 0.16})$. Overall, our results are consistent with low- and high-mass quiescent galaxies following different quenching pathways. The evolution of low-mass quiescent galaxies is qualitatively consistent with the expectations of external/environmental quenching (e.g. ram-pressure stripping). In contrast, the evolution of high-mass quiescent galaxies is consistent with internal/mass quenching (e.g. active galactic nucleus feedback) followed by size growth driven by minor mergers.