Buell T. Jannuzi

A Luminosity Function of Lyman-alpha Emitting Galaxies at Redshift 4.5

We present a catalog of 59 -->z ? 4.5 Ly?-emitting galaxies spectroscopically confirmed in a campaign of Keck DEIMOS follow-up observations to candidates selected in the Large Area Ly? (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 Ly?-emitting galaxies in the 0.7 deg2 covered by the LALA imaging. As with the Keck LRIS sample, we find that a nonnegligible fraction of the confirmed Ly? lines have rest-frame equivalent widths ( -->W?rest) that exceed the maximum predicted for normal stellar populations: 17%-31% (93% confidence) of the detected galaxies show -->W?rest > 190 ?, and 12%-27% (90% confidence) show -->W?rest > 240 ?. We construct a luminosity function of -->z ? 4.5 Ly? emission lines for comparison to Ly? luminosity functions spanning -->3.1 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.