Medium-resolution spectroscopy of FORJ0332-3557: Probing the interstellar medium and stellar populations of a lensed Lyman-break galaxy at z=3.77

TL;DR

This study presents medium-resolution UV spectroscopy of a gravitationally lensed galaxy at z=3.77, revealing insights into its stellar populations, outflows, and interstellar medium properties, including evidence of a young starburst and Wolf-Rayet stars.

Contribution

First detailed UV spectral analysis of a lensed Lyman-break galaxy at z=3.77, providing new insights into its stellar populations and interstellar medium characteristics.

Findings

Detected a young stellar population less than 30 Ma

Observed outflows with an expansion velocity of about 270 km/s

Identified Wolf-Rayet stars indicating a very young starburst

Abstract

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 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 30 Ma, with an extinction of A(V)=0.5 mag and an extinction-corrected star formation rate SFR(UV) of 200-300 Msun/a. The Lyman-alpha line exhibits a damped profile in absorption produced by a column density of about N(HI) = (2.5+_1.0) 10^21 atoms/cm^2, superimposed on an emission line shifted both spatially (0.5 arcsec with respect to the UV continuum source) and in velocity space (+830 km/s with respect to the low-ionisation absorption lines from its interstellar medium), a clear signature of outflows with an expansion velocity of about 270 km/s. A strong emission line from HeII 164.04nm indicates the presence of Wolf-Rayet stars and reinforces the interpretation of a very young starburst. The metallic lines indicate sub-solar abundances of elements Si, Al, and C in the ionised gas phase.