Abstract

We selected 40 candidate Lyα-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 arcmin2, 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 h70 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 × 108 h70 2 M⊙ and minimal dust extinction, AV ≲ 0.1. Inferred star formation rates are ≃6 h70 -2 M⊙ yr-1, yielding a cosmic star formation rate density of 2 × 10-3 h70 M⊙ yr-1 Mpc-3. None of our LAE candidates show evidence for rest-frame emission-line equivalent widths EWrest > 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.