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 HST it is
now possible to measure this beyond the local Universe. Here we present the
spatial distribution of Halpha emission for a sample of 54 strongly
star-forming galaxies at z~1 in the 3D-HST Treasury survey. By stacking the
Halpha emission we find that star formation occurred in approximately
exponential distributions at z~1, with median Sersic index of n=1.0+-0.2. The
stacks are elongated with median axis ratios of b/a=0.58+-0.09 in Halpha,
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 to 330 km/s. 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(Halpha)~100 Angstroms out to the solar orbit and they have star formation
surface densities above the threshold for driving galactic scale winds.
