SDSS J1059+4251, a highly magnified z ~ 2.8 star-forming galaxy: ESI
  observations of the rest-frame UV spectrum
  Detailed analyses of high-redshift galaxies are challenging due to their
faintness, but this difficulty can be overcome with gravitational lensing, in
which the magnification of the flux enables high signal-to-noise ratio (S/N)
spectroscopy. We present the rest-frame ultraviolet (UV) Keck Echellette
Spectrograph and Imager (ESI) spectrum of the newly discovered z = 2.79 lensed
galaxy SDSS J1059+4251. With an observed magnitude F814W = 18.8 and a
magnification factor \mu = 31 \pm 3, J1059+4251 is both highly magnified and
intrinsically luminous, about two magnitudes brighter than M* at z ~ 2-3. With
stellar mass M* = (3.22 \pm 0.20) \times 10^10 M_sun, UV star formation rate
SFR=50 \pm 7 M_sun yr^-1, and stellar metallicity Z*~ 0.15-0.5 Z_sun,
J1059+4251 is typical of bright star-forming galaxies at similar redshifts.
Thanks to the high S/N and the spectral resolution of the ESI spectrum, we are
able to separate the interstellar and stellar features and derive properties
that would be inaccessible without the aid of the lensing. We find evidence of
a gas outflow with speeds up to -1000 km s^-1, and of an inflow that is
probably due to accreting material seen along a favorable line of sight. We
measure relative elemental abundances from the interstellar absorption lines
and find that alpha-capture elements are overabundant compared to iron-peak
elements, suggestive of rapid star formation. However, this trend may also be
affected by dust depletion. Thanks to the high data quality, our results
represent a reliable step forward in the characterization of typical galaxies
at early cosmic epochs.
