The Size Evolution of Passive Galaxies: Observations from the Wide Field Camera 3 Early Release Science Program

TL;DR

This study investigates how the sizes of passive galaxies at redshifts 1 to 2 evolve over time, revealing a strong dependence on stellar mass and providing insights into galaxy dynamical evolution.

Contribution

It presents new observational evidence of size evolution in passive galaxies at high redshift, highlighting the mass dependence of this evolution.

Findings

Size evolution is more rapid for more massive galaxies.

The size evolution parameter alpha correlates with stellar mass.

Passive galaxies at z~2 are significantly smaller than their local counterparts.

Abstract

We present results on the size evolution of passively evolving galaxies at 1<z<2 drawn from the Wide Field Camera 3 Early Release Science program. Our sample was constructed using an analog to the passive BzK selection criterion, which isolates galaxies with little or no on-going star formation at z>1.5. We identify 30 galaxies in ~40 square arcmin to H<25 mag. We supplement spectroscopic redshifts from the literature with photometric redshifts determined from the 15-band photometry from 0.22-8 micron. We determine effective radii from Sersic profile fits to the H-band image using an empirical PSF. We find that size evolution is a strong function of stellar mass, with the most massive (M* ~ 10^11 Msol) galaxies undergoing the most rapid evolution from z~2 to the present. Parameterizing the size evolution as (1+z)^{-alpha}, we find a tentative scaling between alpha and stellar mass of alpha ~ -1.8+1.4 log(M*/10^9 Msol). We briefly discuss the implications of this result for our understanding of the dynamical evolution of the red galaxies.