GEMS: The Size Evolution of Disk Galaxies

TL;DR

This study investigates the evolution of disk galaxy sizes and properties since redshift 1.1, revealing significant changes in luminosity and color but little change in stellar mass size relation, challenging simple theoretical models.

Contribution

It provides a detailed analysis of disk galaxy evolution, combining HST imaging with photometric redshifts, and finds weak evolution in stellar mass-size relation contrary to naive expectations.

Findings

Strong evolution in magnitude-size relation with brightening by 1 mag since z=1.

Disks at z=1 are bluer and have lower mass-to-light ratios.

Weak or no evolution in stellar mass and size relation for galaxies with log(M)>10.

Abstract

We combine HST imaging from the GEMS survey with photometric redshifts from COMBO-17 to explore the evolution of disk-dominated galaxies since z<1.1. The sample is comprised of all GEMS galaxies with Sersic indices n<2.5, derived from fits to the galaxy images. We account fully for selection effects through careful analysis of image simulations; we are limited by the depth of the redshift and HST data to the study of galaxies with absolute magnitudes M(V)<-20, or equivalently stellar masses log(M)>10. We find strong evolution in the magnitude-size scaling relation for galaxies with M(V)<-20, corresponding to a brightening of 1 mag per sqarcsec in rest-frame V-band by z=1. Yet, disks at a given absolute magnitude are bluer and have lower stellar mass-to-light ratios at z=1 than at the present day. As a result, our findings indicate weak or no evolution in the relation between stellar mass and effective disk size for galaxies with log(M)>10 over the same time interval. This is strongly inconsistent with the most naive theoretical expectation, in which disk size scales in proportion to the halo virial radius, which would predict that disks are a factor of two denser at fixed mass at z=1. The lack of evolution in the stellar mass-size relation is consistent with an ``inside-out'' growth of galaxy disks on average (galaxies increasing in size as they grow more massive), although we cannot rule out more complex evolutionary scenarios.