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 {r}_1/2,{maj}=1.02+/- 0.29 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 {r}_e=7.07{(1+z)}^-0.89 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 ({r}_e\propto {(1+z)}^{-1.2+/- 0.06}). Therefore, we conclude the LBGs likely represent a subset of highly star-forming galaxies that exhibit rapid size growth at z > 4.