CLEAR: The Evolution of Spatially Resolved Star Formation in Galaxies between 0.5 ≲ z ≲ 1.7 Using Hα Emission Line Maps

Abstract

Using spatially resolved Hα emission line maps of star-forming galaxies, we study the spatial distribution of star formation over a wide range in redshift (0.5 ≲ z ≲ 1.7). Our z ∼ 0.5 measurements come from deep Hubble Space Telescope (HST) Wide Field Camera 3 G102 grism spectroscopy obtained as part of the CANDELS Lyα Emission at Reionization Experiment. For star-forming galaxies with log(M */M ⊙) ≥ 8.96, the mean Hα effective radius is 1.2 ± 0.1 times larger than that of the stellar continuum, implying inside-out growth via star formation. This measurement agrees within 1σ with those measured at z ∼ 1 and z ∼ 1.7 from the 3D-HST and KMOS3D surveys, respectively, implying no redshift evolution. However, we observe redshift evolution in the stellar mass surface density within 1 kpc (Σ1kpc). Star-forming galaxies at z ∼ 0.5 with a stellar mass of log(M */M ⊙) = 9.5 have a ratio of Σ1kpc in Hα relative to their stellar continuum that is lower by (19 ± 2)% compared to z ∼ 1 galaxies. Σ1kpc,Hα /Σ1kpc,Cont decreases toward higher stellar masses. The majority of the redshift evolution in Σ1kpc,Hα /Σ1kpc,Cont versus stellar mass stems from the fact that log(Σ1kpc,Hα ) declines twice as much as log(Σ1kpc,Cont) from z ∼ 1 to 0.5 (at a fixed stellar mass of log(M */M ⊙) = 9.5). By comparing our results to the TNG50 cosmological magneto-hydrodynamical simulation, we rule out dust as the driver of this evolution. Our results are consistent with inside-out quenching following in the wake of inside-out growth, the former of which drives the significant drop in Σ1kpc,Hα from z ∼ 1 to z ∼ 0.5.