A Luminosity Function of Lyman Alpha Emitting Galaxies at Redshift 4.5

We present a catalog of 59 z approximate to 4.5 Ly alpha-emitting galaxies spectroscopically confirmed in a campaign of Keck DEIMOS follow-up observations to candidates selected in the Large Area Ly alpha ( 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 similar to 76%. Together with our previous sample of Keck LRIS confirmations, the 59 sources confirmed herein bring the total catalog to 73 spectroscopically confirmed z approximate to 4.5 Ly alpha-emitting galaxies in the approximate to 0.7 deg(2) covered by the LALA imaging. As with the Keck LRIS sample, we find that a nonnegligible fraction of the confirmed Ly alpha lines have rest-frame equivalent widths (W-lambda(rest)) that exceed the maximum predicted for normal stellar populations: 17%-31%( 93% confidence) of the detected galaxies show W-lambda(rest) > 190 angstrom, and 12%-27% ( 90% confidence) show W-lambda(rest) > 240 angstrom. We construct a luminosity function of z approximate to 4.5 Ly alpha emission lines for comparison to Ly alpha luminosity functions spanning 3.1 < z < 6.6. We find no significant evidence for Ly alpha luminosity function evolution from z approximate to 3 to z approximate to 6. This result supports the conclusion that the intergalactic medium remains largely reionized from the local universe out to z approximate to 6.5. It is somewhat at odds with the pronounced drop in the cosmic star formation rate density recently measured between z similar to 3 and z similar to 6 in continuum-selected Lyman-break galaxies, and therefore potentially sheds light on the relationship between the two populations.