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

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 $88_{-20}^{+4}$ per cent within 0.5$r_{500}$, significantly enhanced over the field value of $20_{-2}^{+2}$ per cent at $z\sim 2$. 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 $63_{-24}^{+31}$ per cent larger at a fixed mass of $M_{\star }=5\times 10^{10}{M}_{\odot }$. 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.

9 pages, 7 figures, accepted for publication in MNRAS

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