GEMS: The Surface Brightness and Surface Mass Density Evolution of Disk Galaxies

Abstract

We combine HST imaging from the GEMS survey with photometric redshifts from\nCOMBO-17 to explore the evolution of disk-dominated galaxies since z<1.1. The\nsample is comprised of all GEMS galaxies with Sersic indices n<2.5, derived\nfrom fits to the galaxy images. We account fully for selection effects through\ncareful analysis of image simulations; we are limited by the depth of the\nredshift and HST data to the study of galaxies with absolute magnitudes\nM(V)<-20, or equivalently stellar masses log(M)>10. We find strong evolution in\nthe magnitude-size scaling relation for galaxies with M(V)<-20, corresponding\nto a brightening of 1 mag per sqarcsec in rest-frame V-band by z=1. Yet, disks\nat a given absolute magnitude are bluer and have lower stellar mass-to-light\nratios at z=1 than at the present day. As a result, our findings indicate weak\nor no evolution in the relation between stellar mass and effective disk size\nfor galaxies with log(M)>10 over the same time interval. This is strongly\ninconsistent with the most naive theoretical expectation, in which disk size\nscales in proportion to the halo virial radius, which would predict that disks\nare a factor of two denser at fixed mass at z=1. The lack of evolution in the\nstellar mass-size relation is consistent with an ``inside-out'' growth of\ngalaxy disks on average (galaxies increasing in size as they grow more\nmassive), although we cannot rule out more complex evolutionary scenarios.\n