The Mass-Radius Relation for Star-Forming Galaxies at z ~ 1.5-3.0

TL;DR

This study investigates the size evolution of star-forming galaxies at redshifts 1.5 to 3.0, revealing that their half-light radii grow over cosmic time and are smaller than local counterparts, aligning with models including feedback effects.

Contribution

It provides new measurements of the stellar mass-radius relation at high redshift using HST imaging, highlighting the evolution of galaxy sizes over cosmic time.

Findings

Average half-light radius ~1.66 kpc at z~2

Size evolution follows (1+z)^{-1.42}

High-redshift galaxies are smaller than local late-type galaxies

Abstract

We present early results from a Hubble Space Telescope (HST) WFC3/IR imaging survey of star-forming galaxies in the redshift range 1.5 < z < 3.0. When complete, this survey will consist of 42 orbits of F160W imaging distributed amongst 10 survey fields on the line of sight to bright background QSOs, covering 65 arcmin^2 to a depth of 27.9 AB with a PSF FWHM of 0.18". In this contribution, we use a subset of these fields to explore the evolution of the galactic stellar mass-radius relation for a magnitude-limited sample of 102 spectroscopically-confirmed star forming galaxies (<SFR> ~ 30 Msun/yr) with stellar mass M* ~ 10^{10} Msun. Although the light profile of these galaxies often has an irregular, multi-component morphology, it is typically possible to describe the brightest component with a Sersic profile of index n ~ 1. The circularized half-light radius r_e of the brightest component is on average <r_e> = 1.66 \pm 0.79 kpc (i.e., ~ 50-70% the size of local late-type galaxies with similar stellar mass), consistent with recent theoretical models that incorporate strong feedback from star forming regions. The mean half-light radius increases with stellar mass and, at fixed stellar mass, evolves with cosmic time as ~ (1+z)^{-1.42}, suggesting that high redshift star forming galaxies may evolve onto the local stellar mass-radius relation by redshift z ~ 1.