WHERE STARS FORM: INSIDE-OUT GROWTH AND COHERENT STAR FORMATION FROM HST Hα MAPS OF 3200 GALAXIES ACROSS THE MAIN SEQUENCE AT 0.7 < z < 1.5

Abstract

ABSTRACT We present H α maps at 1 kpc spatial resolution for star-forming galaxies at z ∼ 1, made possible by the Wide Field Camera 3 grism on Hubble Space Telescope ( HST ). Employing this capability over all five 3D- HST /CANDELS fields provides a sample of 3200 galaxies enabling a division into subsamples based on stellar mass and star formation rate (SFR). By creating deep stacked H α images, we reach surface brightness limits of 1 × 10 −18 erg s −1 cm −2 arcsec −2 , allowing us to map the distribution of ionized gas to ∼10 kpc for typical L * galaxies at this epoch. We find that the spatial extent of the H α distribution increases with stellar mass as kpc. The H α emission is more extended than the stellar continuum emission, consistent with inside-out assembly of galactic disks. This effect grows stronger with mass as . We map the H α distribution as a function of SFR(IR+UV) and find evidence for “coherent star formation” across the SFR– M * plane: above the main sequence (MS), H α is enhanced at all radii; below the MS, H α is depressed at all radii. This suggests that at all masses the physical processes driving the enhancement or suppression of star formation act throughout the disks of galaxies. At high masses ( ), above the MS, H α is particularly enhanced in the center, potentially building bulges and/or supermassive black holes. Below the MS, a strong central dip in the EW(H α ), as well as the inferred specific SFR, appears. Importantly, though, across the entirety of the SFR– M * plane, the absolute SFR as traced by H α is always centrally peaked, even in galaxies below the MS.