2008MNRAS.386.2065C

We recently reported the discovery of FORJ0332-3557, a lensed Lyman-break galaxy at z = 3.77 in a remarkable example of strong galaxy-galaxy gravitational lensing. We present here a medium-resolution rest-frame ultraviolet (UV) spectrum of the source, which appears to be similar to the well-known Lyman-break galaxy MS1512-cB58 at z = 2.73. The spectral energy distribution is consistent with a stellar population of less than 30Ma, with an extinction of A_v= 0.5 mag and an extinction-corrected star formation rate SFR_UV of 200- 300h^–1₇₀M_☉a^–1. The Lyα line exhibits a damped profile in absorption produced by a column density of about N_Hi= (2.5±1.0)x10²¹/cm2, superimposed on an emission line shifted both spatially (0.5 arcsec with respect to the UV continuum source) and in velocity space (+830km/s with respect to the low-ionization absorption lines from its interstellar medium), a clear signature of outflows with an expansion velocity of about 270km/s. A strong emission line from HeII λ164.04 nm indicates the presence of Wolf-Rayet stars and reinforces the interpretation of a very young starburst. The metallic lines indicate subsolar abundances of elements Si, Al and C in the ionized gas phase.