Dust in the Wind: Composition and Kinematics of Galaxy Outflows at the
  Peak Epoch of Star Formation
  Galactic-scale outflows regulate the stellar mass growth and chemical
enrichment of galaxies, yet key outflow properties such as the chemical
composition and mass loss rate remain largely unknown. We address these
properties with Keck/ESI echellete spectra of nine gravitationally lensed z=2-3
star forming galaxies, probing a range of absorption transitions. Interstellar
absorption in our sample is dominated by outflowing material, with typical
velocities -150 km/s. Approximately 80% of the total column density is
associated with a net outflow. Mass loss rates in the low ionization phase are
comparable to or in excess of the star formation rate, with total outflow rates
likely higher when accounting for ionized gas. Of order half of the heavy
element yield from star formation is ejected in the low ionization phase,
confirming that outflows play a critical role in regulating galaxy chemical
evolution. Covering fractions vary and are in general non-uniform, with most
galaxies having incomplete covering by the low ions across all velocities. Low
ion abundance patterns show remarkably little scatter, revealing a distinct
"chemical fingerprint" of outflows. Gas phase Si/Fe abundances are
significantly super-solar ([Si/Fe]$\gtrsim$0.4) indicating a combination of
$\alpha$-enhancement and dust depletion. Derived properties are comparable to
the most kinematically broad, metal-rich, and depleted intergalactic absorption
systems at similar redshifts, suggesting that these extreme systems are
associated with galactic outflows at impact parameters conservatively within a
few tens of kpc. We discuss implications of the abundance patterns in z=2-3
galaxies and the role of outflows at this epoch.
