A Compact Group of Galaxies at z = 2.48 hosting an AGN-Driven Outflow

TL;DR

This study reports on a compact galaxy group at z=2.48, featuring a massive quiescent galaxy, merging galaxies with an AGN, and evidence of outflows driven by radio jets or AGN activity.

Contribution

It provides detailed observations of a high-redshift compact galaxy group with an extreme quiescent galaxy and AGN-driven outflows, highlighting galaxy interactions and feedback mechanisms.

Findings

Discovery of a massive quiescent compact galaxy at high redshift.

Detection of broad emission lines indicating outflows near the AGN.

Evidence of radio jet-driven outflows extending beyond the merging system.

Abstract

We present observations of a remarkable compact group of galaxies at $z = 2.48$. Four galaxies, all within 40 kpc of each other, surround a powerful high redshift radio source. This group comprises two compact red passive galaxies and a pair of merging galaxies. One of the red galaxies, with an apparent stellar mass of $3.6\times10^{11} M_{\odot}$ and an effective radius of 470 pc, is one of the most extreme examples of a massive quiescent compact galaxy found so far. One of the pair of merging galaxies hosts the AGN producing the large powerful radio structure. The merger is massive and enriched, consistent with the mass-metallicity relation expected at this redshift. Close to the merging nuclei, the emission lines exhibit broad and asymmetric profiles that suggest outflows powered either by a very young expanding radio jet or by AGN radiation. At $\gtrsim 50$ kpc from the system, we found a fainter extended-emission region that may be a part of a radio jet-driven outflow.