AGN Feedback in Quiescent Galaxies at Cosmic Noon Traced by Ionized Gas Emission

TL;DR

This study reveals that low luminosity AGN are prevalent in high-redshift quiescent galaxies, potentially influencing star formation quenching and galaxy evolution from Cosmic Noon to the present.

Contribution

It provides the first representative evidence that low luminosity AGN are common in quiescent galaxies at high redshift, impacting galaxy quenching processes.

Findings

75% of quiescent galaxies show ionized gas emission lines

Most gas ionized by AGN activity despite no X-ray detection

Presence of ionized and neutral outflows in some galaxies

Abstract

We analyze ionized gas emission lines in deep rest-frame optical spectra of 16 quiescent galaxies at redshift $1.7<z<3.5$ observed with JWST/NIRSpec by the Blue Jay survey. Robust detection of emission lines in $75\%$ of the sample indicates the presence of ongoing ionizing sources in this passive population. The H$\alpha$ line luminosities confirm that the population is quiescent, with star formation rates that are at least ten times lower than the main sequence of star formation. The quiescent sample is clearly separate from the star-forming population in line diagnostic diagrams, and occupies a region usually populated by active galactic nuclei (AGN). Analysis of the observed line ratios, equivalent widths, and velocity dispersions leads us to conclude that in most cases the gas is ionized by AGN activity, despite the lack of X-ray detections. A subset of the sample also hosts ionized and/or neutral outflows. Our results show, for the first time using a representative sample, that low luminosity AGN are extremely common among quiescent galaxies at high redshift. These low luminosity AGN may play a key role in quenching star formation and in maintaining massive galaxies quiescent from Cosmic Noon to $z\sim0$.