An ancient massive quiescent galaxy found in a gas-rich z ~ 3 group

TL;DR

Deep observations uncovered a massive, ancient quiescent galaxy at z~3 within a gas-rich group, challenging assumptions about galaxy quenching and evolution in dense environments.

Contribution

This study presents the discovery of one of the oldest known galaxies at z~3, showing passive evolution and early quenching in a dense, gas-rich environment, which is a novel insight.

Findings

The galaxy has a stellar age of about 1.6 Gyr, indicating early formation.

It resides in a dense group with extensive cold gas reservoirs.

Quenching can occur without shutting down gas accretion.

Abstract

Deep ALMA and HST observations reveal the presence of a quenched massive galaxy within the $z=2.91$ galaxy group RO-1001. With a mass-weighted stellar age of $1.6 \pm 0.4 \,$Gyr this galaxy is one of the oldest known at $z\sim3$, implying that most of its $10^{11}\rm \, M_{\odot}$ of stars were rapidly formed at $z>6$--8. This is a unique example of the predominantly passive evolution of a galaxy over at least $3<z<6$ following its high-redshift quenching and a smoking-gun event pointing to the early imprint of an age-environment relation. At the same time, being in a dense group environment with extensive cold-gas reservoirs as betrayed by a giant Ly$\alpha$ halo, the existence of this galaxy demonstrates that gas accretion shutdown is not necessary for quenching and its maintenance.