THE RADIAL DISTRIBUTION OF STAR FORMATION IN GALAXIES AT z ∼ 1 FROM THE 3D-HST SURVEY

The assembly of galaxies can be described by the distribution of their star formation as a function of cosmic time. Thanks to the WFC3 grism on the Hubble Space Telescope (HST) it is now possible to measure this beyond the local Universe. Here we present the spatial distribution of Hα emission for a sample of 54 strongly star-forming galaxies at z ∼ 1 in the 3D-HST Treasury survey. By stacking the Hα emission, we find that star formation occurred in approximately exponential distributions at z ∼ 1, with a median Sérsic index of n = 1.0 ± 0.2. The stacks are elongated with median axis ratios of b/a = 0.58 ± 0.09 in Hα consistent with (possibly thick) disks at random orientation angles. Keck spectra obtained for a subset of eight of the galaxies show clear evidence for rotation, with inclination corrected velocities of 90–330 km s−1. The most straightforward interpretation of our results is that star formation in strongly star-forming galaxies at z ∼ 1 generally occurred in disks. The disks appear to be “scaled-up” versions of nearby spiral galaxies: they have EW(Hα) ∼ 100 Å out to the solar orbit and they have star formation surface densities above the threshold for driving galactic scale winds.