The Spatial Extent and Distribution of Star Formation in 3D-HST Mergers
  at z~1.5
  We present an analysis of the spatial distribution of star formation in a
sample of 60 visually identified galaxy merger candidates at z>1. Our sample,
drawn from the 3D-HST survey, is flux-limited and was selected to have high
star formation rates based on fits of their broad-band, low spatial resolution
spectral energy distributions. It includes plausible pre-merger (close pairs)
and post-merger (single objects with tidal features) systems, with total
stellar masses and star formation rates derived from multi-wavelength
photometry. Here we use near-infrared slitless spectra from 3D-HST which
produce Halpha or [OIII] emission line maps as proxies for star-formation maps.
This provides a first comprehensive high-resolution, empirical picture of where
star formation occurred in galaxy mergers at the epoch of peak cosmic star
formation rate. We find that detectable star formation can occur in one or both
galaxy centres, or in tidal tails. The most common case (58%) is that star
formation is largely concentrated in a single, compact region, coincident with
the centre of (one of) the merger components. No correlations between star
formation morphology and redshift, total stellar mass, or star formation rate
are found. A restricted set of hydrodynamical merger simulations between
similarly massive and gas-rich objects implies that star formation should be
detectable in both merger components, when the gas fractions of the individual
components are the same. This suggests that z~1.5 mergers typically occur
between galaxies whose gas fractions, masses, and/or star formation rates are
distinctly different from one another.
