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

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,=,aj) = 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 4 (r_e ∝ (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.

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