Abstract

" We selected 40 candidate Ly?-emitting galaxies (LAEs) at z ? 3.1 with observed-frame equivalent widths greater than 150 Å and inferred emission-line fluxes above 2.5 × 10 -17 ergs cm -2 s -1 from deep narrowband and broadband MUSYC images of the Extended Chandra Deep Field South. Covering 992 arcmin 2, this is the largest ""blank field"" surveyed for LAEs at z ? 3, allowing an improved estimate of the space density of this population of (3 ±1) × 10 -4 h 70 3 Mpc -3. Spectroscopic follow-up of 23 candidates yielded 18 redshifts, all at z ? 3.1. Over 80% of the LAEs are dimmer in continuum magnitude than the typical Lyman break galaxy (LEG) spectroscopic limit of R = 25.5 (AB), with a median continuum magnitude R ? 27 and very blue continuum colors, V-z ? 0. Over 80% of the LAEs have the right UVR colors to be selected as LBGs, but only 10% also have R ? 25.5. Stacking the UBVRIzJK fluxes reveals that LAEs have stellar masses ?5 × 10 8 h 70 2 M? and minimal dust extinction, A V ? 0.1. Inferred star formation rates are ?6 h 70 -2 M? yr -1, yielding a cosmic star formation rate density of 2 × 10 -3 h 70 M? yr -1 Mpc -3. None of our LAE candidates show evidence for rest-frame emission-line equivalent widths EW rest > 240 Å that might imply a nonstandard initial mass function. One candidate is detected by Chandra, implying an AGN fraction of 2% ± 2% for LAE candidate samples. In summary, LAEs at z ? 3 have rapid star formation, low stellar mass, little dust obscuration, and no evidence for a substantial AGN component. © 2006. The American Astronomical Society. All rights reserved. "