The discovery of the most UV-Lya luminous star-forming galaxy: a young,
  dust- and metal-poor starburst with QSO-like luminosities
  We report the discovery of BOSS-EUVLG1 at z=2.469, by far the most luminous,
almost un-obscured star-forming galaxy known at any redshift. First classified
as a QSO within the Baryon Oscillation Spectroscopic Survey, follow-up
observations with the Gran Telescopio Canarias reveal that its large
luminosity, MUV = -24.40 and log(L_Lya/erg s-1) = 44.0, is due to an intense
burst of star-formation, and not to an AGN or gravitational lensing.
BOSS-EUVLG1 is a compact (reff = 1.2 kpc), young (4-5 Myr) starburst with a
stellar mass log(M*/Msun) = 10.0 +/- 0.1 and a prodigious star formation rate
of ~1000 Msun yr-1. However, it is metal- and dust-poor (12+log(O/H) = 8.13 +/-
0.19, E(B-V) = 0.07, log(LIR/LUV) < -1.2), indicating that we are witnessing
the very early phase of an intense starburst that has had no time to enrich the
ISM. BOSS-EUVLG1 might represent a short-lived (<100 Myrs), yet important phase
of star-forming galaxies at high redshift that has been missed in previous
surveys. Within a galaxy evolutionary scheme, BOSS-EUVLG1 could likely
represent the very initial phases in the evolution of massive quiescent
galaxies, even before the dusty star-forming phase.
