The Radial Distribution of Star Formation in Galaxies at z~1 from the 3D-HST Survey

TL;DR

This study reveals that at z~1, strongly star-forming galaxies predominantly have disk-like structures with exponential star formation distributions, similar to scaled-up versions of local spiral galaxies, confirmed by Halpha emission and rotation data.

Contribution

It provides the first detailed analysis of the spatial distribution of star formation in z~1 galaxies using Halpha emission, demonstrating their disk-like nature and rotational support.

Findings

Star formation at z~1 occurs in exponential disk-like structures.

Galaxies show signs of rotation with velocities up to 330 km/s.

Star formation surface densities are high enough to drive galactic winds.

Abstract

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.