A Population of Faint Extended Line Emitters and the Host Galaxies of Optically Thick QSO Absorption Systems

TL;DR

This study identifies faint, extended Lyman-alpha emitters at high redshift, likely representing the host galaxies of optically thick QSO absorption systems, revealing their properties and potential origins.

Contribution

It presents the first deep long-slit survey detecting faint Lyman-alpha emitters and links them to the host galaxies of Damped Lyman-alpha systems at high redshift.

Findings

Detected 27 faint Lyman-alpha emitters with high number density.

Most emitters are likely Lyman-alpha, associated with DLA host galaxies.

Star formation rates are low, possibly dominated by cooling radiation.

Abstract

We have conducted a long slit search for low surface brightness Lyman-alpha emitters at redshift 2.67 < z < 3.75. A 92 hour long exposure with VLT/FORS2 down to a 1-sigma surface brightness detection limit of 8x10^-20 erg/cm2/s/sqarcsec yielded a sample of 27 single line emitters with fluxes of a few times 10^-18 erg/s/cm2. We present arguments that most objects are indeed Lyman-alpha. The large comoving number density, the large covering factor, dN/dz ~ 0.2-1, and the often extended Lyman-alpha emission suggest that the emitters be identified with the elusive host population of damped Lyman-alpha systems (DLAS) and high column density Lyman limit systems. A small inferred star formation rate, perhaps supplanted by cooling radiation, appears to energetically dominate the Lyman-alpha emission, and is consistent with the low metallicity, low dust content, and theoretically inferred low masses of DLAS, and with the relative lack of success of earlier searches for their optical counterparts. (abridged)