The Physical Nature of Lyα-emitting Galaxies at z = 3.1 (original) (raw)
2006, The Astrophysical Journal
We selected 40 candidate Lyman Alpha Emitting galaxies (LAEs) at z ≃ 3.1 with observed frame equivalent widths >150Å and inferred emission line fluxes > 2.5 × 10 −17 ergs cm −2 s −1 from deep narrow-band 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 3 70 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 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 UV R colors to be selected as Lyman break galaxies, but only 10% also have R ≤ 25.5. Stacking the UBV RIzJK fluxes reveals that LAEs have stellar masses ≃ 5 × 10 8 h −2 70 M ⊙ and minimal dust extinction, A V 0.1. Inferred star formation rates are ≃6h −2 70 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 restframe emission line equivalent widths EW rest >240Å which might imply a non-standard IMF. 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. 1
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