CANDELS Observations of the Structural Properties and Evolution of Galaxies in a Cluster at z=1.62

TL;DR

This study examines the structural properties and evolution of galaxies in a z=1.62 proto-cluster using Hubble data, revealing slower size growth compared to field galaxies and evidence of extended stellar disks.

Contribution

It provides new insights into the size evolution and morphological features of cluster galaxies at high redshift, highlighting the impact of dense environments on galaxy development.

Findings

Cluster galaxies have larger sizes than field galaxies at fixed mass.

Size evolution of quiescent cluster galaxies is slow, following (1+z)^(-0.6+/-0.1).

Cluster galaxies show signs of extended stellar disks and require dry mergers for evolution.

Abstract

We discuss the structural and morphological properties of galaxies in a z=1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology relation: galaxies with colors of quiescent stellar populations generally have morphologies consistent with spheroids, and galaxies with colors consistent with ongoing star formation have disk-like and irregular morphologies. The size distribution of the quiescent cluster galaxies shows a deficit of compact (< 1kpc), massive galaxies compared to CANDELS field galaxies at z=1.6. As a result the cluster quiescent galaxies have larger average effective sizes compared to field galaxies at fixed mass at greater than 90% significance. Combined with data from the literature, the size evolution of quiescent cluster galaxies is relatively slow from z~1.6 to the present, growing as (1+z)^(-0.6+/-0.1). If this result is generalizable, then it implies that physical processes associated with the denser cluster region seems to have caused accelerated size growth in quiescent galaxies prior to z=1.6 and slower subsequent growth at z<1.6 compared to galaxies in the lower density field. The quiescent cluster galaxies at z=1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface-brightness profiles suggest that they contain extended stellar disks. We argue the cluster galaxies require dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk material and to match the relations for ellipticity, stellar mass, size, and color of early-type galaxies in z<1 clusters.