Abstract

For the first time, we study the evolution of the stellar mass-size relation for star-forming galaxies from z similar to 4 to z similar to 7 from Hubble-WFC3/IR camera observations of the HUDF and Early Release Science field. The sizes are measured by determining the best-fit model to galaxy images in the rest-frame 2100 angstrom with the stellar masses estimated from spectral energy distribution fitting to rest-frame optical (from Spitzer/IRAC) and UV fluxes. We show that the stellar mass-size relation of Lyman break galaxies (LBGs) persists, at least to z similar to 5, and the median size of LBGs at a given stellar mass increases toward lower redshifts. For galaxies with stellar masses of 9.5 log(M-*/M-circle dot) 10.4, sizes evolve as (1 + z)(-1.20 +/- 0.11). This evolution is very similar for galaxies with lower stellar masses of 8.6 log(M-*/M-circle dot) 9.5 which is r(e) proportional to (1 + z)(-1.18 +/- 0.10), in agreement with simple theoretical galaxy formation models at high z. Our results are consistent with previous measurements of the LBGs mass-size relation at lower redshifts (z similar to 1-3).