Abstract

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± 3, J1059+4251 is both highly magnified and intrinsically luminous, making it one of the brightest lensed galaxies observed so far. With stellar mass M*= 3.7 x 1010 M☉, star formation rate SFR=73 M☉ yr-1, and stellar metallicity Z*=0.004, 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, which is particularly high in J1059+4251. Thanks to the high data quality, our results represent a reliable step forward in the characterization of typical galaxies at early cosmic epochs.