The discovery of the most UV-Lya luminous star-forming galaxy: a young, dust- and metal-poor starburst with QSO-like luminosities

TL;DR

This paper reports the discovery of BOSS-EUVLG1, the most luminous UV-Lya star-forming galaxy at high redshift, characterized by intense star formation, low dust and metal content, and potential insights into early galaxy evolution.

Contribution

It presents the identification and detailed analysis of a unique, extremely luminous, young, dust- and metal-poor starburst galaxy at z=2.469, revealing a new phase in high-redshift galaxy evolution.

Findings

Most luminous, nearly unobscured star-forming galaxy at any redshift.

Young starburst with high star formation rate (~1000 Msun/yr).

Low metallicity and dust content indicating early evolutionary stage.

Abstract

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.