Spectroscopic Confirmation of Three Redshift [CLC][ITAL]z[/ITAL][/CLC] ≈ 5.7 L[CLC]y[/CLC]α Emitters from the Large-Area Lyman Alpha Survey

Narrow-band searches for Lyman alpha emission are an efficient way ofidentifying star-forming galaxies at high redshifts. We present Keck telescopespectra confirming redshifts z = 5.7 for three objects discovered in the LargeArea Lyman Alpha (LALA) survey at Kitt Peak National Observatory. All three spectra show strong, narrow emission lines with the asymmetricprofile that is characteristically produced in high redshift Lyman alphaemitters by preferential HI absorption in the blue wing of the line. Theseobjects are undetected in deep Bw, V, R, and 6600A narrow-band images from theNOAO Deep Wide-Field Survey and from LALA, as expected from Lyman break andLyman alpha forest absorption at redshift z = 5.7. All three objects show largeequivalent widths (>= 150A in the rest-frame), suggesting at least one of thefollowing: a top-heavy initial mass function, very low stellar metallicity, orthe presence of an active nucleus. We consider the case for an active nucleusto be weak in all three objects due to the limited width of the Lyman alphaemission line (< 500 km/s) and the absence of any other indicator of quasaractivity. The three confirmed high redshift objects were among four spectroscopicallyobserved targets drawn from the sample of 18 candidates presented by Rhoads andMalhotra (2001). Thus, these spectra support the Lyman alpha emitter populationstatistics from our earlier photometric study, which imply little evolution innumber density from z=5.7 to z=4.5 and provide strong evidence that thereionization redshift is greater than 5.7.Comment: Submitted to AJ, June 2002. 15 pages, AASTe