A Keck Survey of Gravitationally-Lensed Star-Forming Galaxies: High
  Spatial Resolution Studies of Kinematics and Metallicity Gradients
  We discuss spatially resolved emission line spectroscopy secured for a total
sample of 15 gravitationally lensed star-forming galaxies at a mean redshift of
$z\simeq2$ based on Keck laser-assisted adaptive optics observations undertaken
with the recently-improved OSIRIS integral field unit (IFU) spectrograph. By
exploiting gravitationally lensed sources drawn primarily from the CASSOWARY
survey, we sample these sub-L$^{\ast}$ galaxies with source-plane resolutions
of a few hundred parsecs ensuring well-sampled 2-D velocity data and resolved
variations in the gas-phase metallicity. Such high spatial resolution data
offers a critical check on the structural properties of larger samples derived
with coarser sampling using multiple-IFU instruments. We demonstrate how
kinematic complexities essential to understanding the maturity of an early
star-forming galaxy can often only be revealed with better sampled data.
Although we include four sources from our earlier work, the present study
provides a more representative sample unbiased with respect to emission line
strength. Contrary to earlier suggestions, our data indicates a more diverse
range of kinematic and metal gradient behavior inconsistent with a simple
picture of well-ordered rotation developing concurrently with established steep
metal gradients in all but merging systems. Comparing our observations with the
predictions of hydrodynamical simulations suggests that gas and metals have
been mixed by outflows or other strong feedback processes, flattening the metal
gradients in early star-forming galaxies.
