A Luminosity Function of Lyα‐emitting Galaxies at z ≈ 4.5

Abstract

We present a catalog of 59 z ≈ 4.5 Lyα-emitting galaxies spectroscopically confirmed in a campaign of Keck DEIMOS follow-up observations to candidates selected in the Large Area Lya (LALA) narrowband imaging survey. We targeted 97 candidates for spectroscopic follow-up; by accounting for the variety of conditions under which we performed spectroscopy, we estimate a selection reliability of ∼76%. Together with our previous sample of Keck LRIS confirmations, the 59 sources confirmed herein bring the total catalog to 73 spectroscopically confirmed z ≈ 4.5 Lyαemitting galaxies in the ≈0.7deg 2 covered by the LALA imaging. As with the Keck LRIS sample, we find that a nonnegligible fraction of the confirmed Lya lines have rest-frame equivalent widths (W γ rest ) that exceed the maximum predicted for normal stellar populations: 17%-31% (93% confidence) of the detected galaxies show W γ rest > 190 Å, and 12%-27% (90%) confidence) show W γ rest > 240 ÅWe construct a luminosity function of z ≈ 4.5 Lyα emission lines for comparison to Lyα luminosity functions spanning 3.1 < z < 6.6. We find no significant evidence for Lyα luminosity function evolution from z ≈ 3 to z ≈ 6. This result supports the conclusion that the intergalactic medium remains largely reionized from the local universe out to z ≈ 6.5. It is somewhat at odds with the pronounced drop in the cosmic star formation rate density recently measured between z ∼ 3 and z ∼ 6 in continuum-selected Lyman-break galaxies, and therefore potentially sheds light on the relationship between the two populations. © 2007. The American Astronomical Society. All rights reserved.