Spectroscopic confirmation of three redshift z ≉ 5.7 Lyα emitters from the Large-Area Lyman Alpha survey

Narrowband searches for Lyalpha emission are an efficient way of identifying star-forming galaxies at high redshifts. We present Keck Telescope spectra confirming redshifts z approximate to 5.7 for three objects discovered in the Large-Area Lyman Alpha ( LALA) survey at Kitt Peak National Observatory. All three spectra show strong, narrow emission lines with the asymmetric pro le that is characteristically produced in high-redshift Lyalpha emitters by preferential H I absorption in the blue wing of the line. These objects are undetected in deep B-W, V, R, and lambda = 6600 Angstrom narrowband images from the NOAO Deep Wide-Field Survey and from LALA, as expected from Lyman break and Lyalpha forest absorption at redshift z approximate to 5.7. All three objects show large equivalent widths (greater than or similar to150 Angstrom in the rest frame), suggesting at least one of the following: a top-heavy initial mass function, very low stellar metallicity, or the presence of an active nucleus. We consider the case for an active nucleus to be weak in all three objects due to the limited width of the Lyalpha emission line ( less than 500 km s(-1)) and the absence of any other indicator of quasar activity. The three confirmed high-redshift objects were among four spectroscopically observed targets drawn from the sample of 18 candidates presented by Rhoads & Malhotra. Thus, these spectra support the Lyalpha emitter population statistics from our earlier photometric study, which imply little evolution in number density from z = 5.7 to 4.5 and provide strong evidence that the reionization redshift is z(r) > 5.7.