Possible environmental quenching in an interacting little red dot pair at $z\sim7$

TL;DR

This study reports the discovery of a $z\sim7$ galaxy group with two red, possibly AGN-hosting galaxies showing signs of recent star formation quenching, likely driven by environmental interactions during reionization.

Contribution

First identification of a $z\\sim7$ galaxy pair with signs of environmental quenching and AGN activity, providing insights into galaxy evolution in the early universe.

Findings

The galaxy pair shows evidence of recent star formation quenching.

One galaxy's SED suggests an active galactic nucleus (AGN) presence.

The proximity indicates interaction-driven star formation and quenching.

Abstract

We report the discovery of a $z\sim7$ group of galaxies that contains two little red dots (LRDs) just 3.3 kpc apart, along with three potential satellite galaxies, as part of the Canadian NIRISS Unbiased Cluster Survey (CANUCS). The spectral energy distributions (SEDs) of this LRD pair show evidence of a Balmer break, consistent with a recent ($\sim 100$ Myr) quenching of star formation. In contrast, the satellites are compatible with a recent-onset ($\sim 100$ Myr), ongoing burst of star formation. LRD1's SED is consistent with a dust-free active galactic nucleus (AGN) being the source of the UV excess in the galaxy. The optical continuum would be powered by the emission from an obscured post-starburst and the AGN at a subdominant level. LRD2's SED is more ambiguous, but it could also be indicative of a dust-free AGN. In this scenario, these LRDs would be massive ($M_\star\sim10^{10}\,M_\odot$) and dusty (A(V) $>1$ mag) and the three satellites would be lower-mass objects ($M_\star\sim10^{8-9}\,M_\odot$) subject to low dust attenuations. The proximity of the two LRDs suggests that their interaction is responsible for their recent star formation histories, which can be interpreted as environmental bursting and quenching in the epoch of reionization.