Large Size Scatter of Passively Evolving Lensed Galaxies at z~2 in CLASH

TL;DR

This study identifies and analyzes ten passively evolving massive galaxies at redshift z~2, revealing a large scatter in their sizes and providing insights into their structural evolution compared to local early-type galaxies.

Contribution

It presents the first systematic analysis of the size distribution and properties of passively evolving galaxies at z~2 using lensing data, highlighting significant size scatter.

Findings

Nine out of ten galaxies are smaller than local counterparts of similar mass.

Size scales with redshift as re/M^0.56 ∝ (1 + z)^{-1.13}.

Size distribution shows a large scatter, with sizes varying up to five times smaller than local galaxies.

Abstract

In a systematic search over 11 cluster fields from Cluster Lensing And Supernova survey with Hubble (CLASH) we identify ten passively evolving massive galaxies at redshift z~2.We derive the stellar properties of these galaxies using HST WFC3/ACS multiband data, together with Spitzer IRAC observations. We also deduce the optical rest-frame effective radius of these high redshift objects. The derived stellar masses and measured effective radii have been corrected by the lensing magnification factors, which are estimated by simply adopting the spherical NFW model for the foreground cluster lens. The observed near-IR images, obtained by HST WFC3 camera with high spatial resolution and lensed by the foreground clusters, enable us to study the structures of such systems. Nine out of ten galaxies have on average three times smaller effective radius than local ETGs of similar stellar masses, in agreement with previous works at redshift 1.5 < z < 2.5. Combined with literature data for z~2, we find that the mass-normalized effective radius scales with redshift as re/M^0.56 \propto (1 + z)^{-1.13}. We confirm that their size distribution shows a large scatter: from normal size to ~5 times smaller compared to local ETGs with similar stellar masses. The 1-{\sigma} scatter {\sigma}_{logre} of the size distribution is 0.22 and 0.34 at z~1.6 and z~2.1,respectively.The observed large size scatter has to be carefully taken into account in galaxy evolution model predictions.