Widespread Rapid Quenching at Cosmic Noon Revealed by JWST Deep Spectroscopy

Massive quiescent galaxies in the young universe are expected to be quenchedrapidly, but it is unclear whether they all experience starbursts beforequenching and what physical mechanism drives rapid quenching. We study 16massive quiescent galaxies (log(M_⋆/M_⊙) > 10) at z∼2 selectedfrom a representative sample of the Blue Jay survey. We reconstruct their starformation histories by fitting spectral energy distribution models to theJWST/NIRSpec R∼1000 spectra. We find that massive quiescent galaxies canbe split into three categories with roughly equal numbers of galaxies accordingto their SFHs: 1) Relatively old galaxies quenched at early epochs; 2) Galaxiesthat are rapidly and recently quenched after a flat or bursty formation history(depending on the assumed prior); 3) Galaxies that are rapidly and recentlyquenched after a major starburst. Most recently quenched galaxies show neutralgas outflows, probed by blueshifted Na I D absorption, and ionized gasemission, with line ratios consistent with active galactic nucleus (AGN)diagnostics. This suggests that AGN activity drives multi-phase gas outflows,leading to rapid quenching. By tracing back the SFHs of the entire sample, wepredict the number density of massive quiescent galaxies at z=4-6:n=3.0±1.4×10^-5 Mpc^-3. The two oldest massive quiescentgalaxies in our sample appear to have extremely early formation and quenching(z≳6), possibly descendants of early post-starbursts at z>3. Thesegalaxies still show neutral gas reservoirs and low-level star formation,consistent with weak Hα emission, perhaps because the ejective AGNfeedback that caused rapid quenching has weakened over time.