Widespread rapid quenching at cosmic noon revealed by JWST deep spectroscopy

TL;DR

This study uses JWST spectroscopy to analyze 14 massive quiescent galaxies at z~2, revealing diverse star formation histories and evidence that AGN activity drives rapid quenching through multi-phase gas outflows.

Contribution

It provides the first detailed spectral analysis of massive quiescent galaxies at cosmic noon, identifying different quenching pathways and linking AGN activity to rapid galaxy quenching.

Findings

Galaxies split into three SFH categories: old, recently quenched, and post-starburst.

Most recently quenched galaxies show gas outflows and AGN activity.

Predicted number density of massive quiescent galaxies at z=4-6 is (1.5-6.0)×10⁻⁵ Mpc⁻³.

Abstract

Massive quiescent galaxies in the young universe are expected to be quenched rapidly, but it is unclear whether they all experience starbursts before quenching and what physical mechanism drives rapid quenching. We study 14 massive quiescent galaxies ($\log(M_\star/M_\odot) > 10$) at $z\sim2$ selected from a representative sample of the Blue Jay survey. We reconstruct their star formation histories by fitting spectral energy distribution models to the JWST/NIRSpec $R\sim1000$ spectra. We find that massive quiescent galaxies can be split into three categories with roughly equal numbers of galaxies according to their SFHs: 1) Relatively old galaxies quenched at early epochs; 2) Galaxies that are rapidly and recently quenched after a flat or bursty formation history (depending on the assumed prior); 3) Galaxies that are rapidly and recently quenched after a major starburst. Most recently quenched galaxies show neutral gas outflows, probed by blueshifted $\rm Na\,I\,D$ absorption, and ionized gas emission, 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, we predict the number density of massive quiescent galaxies at $z=4-6$: $n=(1.5-6.0)\times10^{-5}\,\rm Mpc^{-3}$. The two old massive quiescent galaxies in our sample appear to have extremely early formation and quenching ($z\gtrsim6$), possibly descendants of early post-starbursts at $z>3$. These galaxies still show neutral gas reservoirs and weak H$\alpha$ emission, perhaps because the ejective AGN feedback that caused rapid quenching has weakened over time.