CLEAR: The Evolution of Spatially Resolved Star Formation in Galaxies between $0.5\lesssim z\lesssim 1.7$ using H$\hat{I}\pm$ Emission Line Maps

Abstract

Using spatially resolved H-alpha emission line maps of star-forming galaxies, we study the evolution of gradients in galaxy assembly over a wide range in redshift ($0.5<z<1.7$). Our $z\sim 0.5$ measurements come from deep Hubble Space Telescope WFC3 G102 grism spectroscopy obtained as part of the CANDELS Lyman-alpha Emission at Reionization (CLEAR) Experiment. For star-forming galaxies with Log$(M_{\ast }/{\mathrm{M}}_{\odot })⩾8.96$, the mean H-alpha effective radius is $1.2\pm 0.1$ times larger than that of the stellar continuum, implying inside-out growth via star formation. This measurement agrees within $1\ddot{I}ƒ$ with those measured at $z\sim 1$ and $z\sim 1.7$ from the 3D-HST and KMOS-3D surveys respectively, implying no redshift evolution. However, we observe redshift evolution in the stellar mass surface density within 1 kiloparsec ($\hat{I}{\pounds }_{1kpc}$). Star-forming galaxies at $z\sim 0.5$ with a stellar mass of Log$(M_{\ast }/{\mathrm{M}}_{\odot })=9.5$ have a ratio of $\hat{I}{\pounds }_{1kpc}$ in H-alpha relative to their stellar continuum that is lower by $(19\pm 2)\%$ compared to $z\sim 1$ galaxies. $\hat{I}{\pounds }_{1\mathrm{kpc},\mathrm{H}\hat{I}\pm }$/$\hat{I}{\pounds }_{1\mathrm{kpc},\mathrm{Cont}}$ decreases towards higher stellar masses. The majority of the redshift evolution in $\hat{I}{\pounds }_{1\mathrm{kpc},\mathrm{H}\hat{I}\pm }$/$\hat{I}{\pounds }_{1\mathrm{kpc},\mathrm{Cont}}$ versus stellar mass stems from the fact that Log($\hat{I}{\pounds }_{1\mathrm{kpc},\mathrm{H}\hat{I}\pm }$) declines twice as much as Log($\hat{I}{\pounds }_{1\mathrm{kpc},\mathrm{Cont}}$) from $z\sim 1$ to 0.5 (at a fixed stellar mass of Log$(M_{\ast }/{\mathrm{M}}_{\odot })=9.5$). 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 $\hat{I}{\pounds }_{1\mathrm{kpc},\mathrm{H}\hat{I}\pm }$ from $z\sim 1$ to $z\sim 0.5$.

25 pages, 12 figures, 4 tables, Submitted to ApJ