Quiescent galaxies in a virialized cluster at redshift 2: Evidence for accelerated size-growth

TL;DR

This study shows that quiescent galaxies in a virialized cluster at redshift 2 are significantly larger and more numerous than in the field, indicating accelerated size growth likely driven by minor mergers.

Contribution

It provides evidence for accelerated size growth of quiescent cluster galaxies at z~2, highlighting environmental effects on galaxy evolution.

Findings

High quiescent fraction (88%) in the cluster compared to the field (20%).

Cluster galaxies are on average 63% larger at fixed mass than field counterparts.

Evidence suggests minor mergers as a mechanism for rapid size evolution.

Abstract

We present an analysis of the galaxy population in XLSSC 122, an X-ray selected, virialized cluster at redshift $z=1.98$. We utilize HST WFC3 photometry to characterize the activity and morphology of spectroscopically confirmed cluster members. The quiescent fraction is found to be $88^{+4}_{-20}$ per cent within 0.5$r_{500}$, significantly enhanced over the field value of $20^{+2}_{-2}$ per cent at $z\sim2$. We find an excess of "bulge-like" quiescent cluster members with Sersic index $n>2$ relative to the field. These galaxies are found to be larger than their field counterparts at 99.6 per cent confidence, being on average $63^{+31}_{-24}$ per cent larger at a fixed mass of $M_\star = 5\times10^{10} M_\odot$. This suggests that these cluster member galaxies have experienced an accelerated size evolution relative to the field at $z>2$. We discuss minor mergers as a possible mechanism underlying this disproportionate size growth.