The Size Evolution of Star-forming Galaxies since z ∼ 7 Using ZFOURGE

Abstract

For the first time, we present the size evolution of a mass-complete (log( M * / M ⊙ ) > 10) sample of star-forming galaxies over redshifts z  = 1–7, selected from the FourStar Galaxy Evolution Survey. Observed H-band sizes are measured from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) Hubble Space Telescope ( HST )/F160W imaging. Distributions of individual galaxy masses and sizes illustrate that a clear mass−size relation exists up to z  ∼ 7. At z  ∼ 7, we find that the average galaxy size from the mass−size relation is more compact at a fixed mass of log( M * / M ⊙ ) = 10.1, with kpc, than at lower redshifts. This is consistent with our results from stacking the same CANDELS HST /F160W imaging, when we correct for galaxy position angle alignment. We find that the size evolution of star-forming galaxies is well fit by a power law of the form kpc, which is consistent with previous works for normal star-formers at 1 <  z  < 4. In order to compare our slope with those derived Lyman break galaxy studies, we correct for different IMFs and methodology and find a slope of −0.97 ± 0.02, which is shallower than that reported for the evolution of Lyman break galaxies (LBGs) at z  > 4 ( ). Therefore, we conclude the LBGs likely represent a subset of highly star-forming galaxies that exhibit rapid size growth at z  > 4.