Early Results from GLASS-JWST. IX. First Spectroscopic Confirmation of Low-mass Quiescent Galaxies at z > 2 with NIRISS

How passive galaxies form, and the physical mechanisms which prevent star formation over long timescales, are some of the most outstanding questions in understanding galaxy evolution. The properties of quiescent galaxies over cosmic time provide crucial information to identify the quenching mechanisms. Passive galaxies have been confirmed and studied out to z ∼ 4, but all of these studies have been limited to massive systems (mostly with $\mathrm{log}({M}_{\mathrm{star}}/{M}_{\odot })\gt 10.8$). Using JWST-NIRISS grism slitless spectroscopic data from the GLASS-JWST Early Release Science program, we present spectroscopic confirmation of two quiescent galaxies at ${z}_{\mathrm{spec}}={2.650}_{-0.006}^{+0.004}$ and ${z}_{\mathrm{spec}}={2.433}_{-0.016}^{+0.032}$ (3σ errors) with stellar masses of $\mathrm{log}({M}_{\mathrm{star}}/{M}_{\odot })={10.59}_{-0.05}^{+0.11}$ and $\mathrm{log}({M}_{\mathrm{star}}/{M}_{\odot })={10.07}_{-0.03}^{+0.06}$ (corrected for magnification factors of μ = 2.0 and μ = 2.1, respectively). The latter represents the first spectroscopic confirmation of the existence of low-mass quiescent galaxies at cosmic noon, showcasing the power of JWST to identify and characterize this enigmatic population.