Lyα-EMITTING GALAXIES AT REDSHIFT z ∼ 4.5 IN THE LALA CETUS FIELD

We present a large sample of Ly alpha-emitting galaxies (LAEs) spectroscopically confirmed at redshift z approximate to 4.5, based on Inamori-Magellan Areal Camera and Spectrograph spectroscopic observations of candidate z approximate to 4.5 Ly alpha-emitting galaxies in the large area Lyman alpha (LALA) narrowband imaging survey Cetus field. We identify 110 of them as z approximate to 4.5 Ly alpha emitters based on single-line detections with no continuum emission blueward of the line. Six foreground galaxies are identified, either based on multiple lines or blueward continuum emission. The Ly alpha confirmation rate varies from < 50% to 76% for candidates selected in different narrowband filters at slightly different redshifts. We find a drop in the LAE density at redshift 4.50 +/- 0.03 from redshift 4.39 to 4.47 by a factor of 66%, which could be a large-scale void in the distribution of star-forming galaxies (similar to 18 Mpc along the line of sight and similar to 80 Mpc across). The sample includes many objects with equivalent widths (EWs) greater than or similar to 200 angstrom. These large EW candidates are spectroscopically confirmed at the same rate as candidates with more modest EWs. A composite spectrum of all 110 confirmed LAEs shows the characteristic asymmetry of the Ly alpha line. It also places new and stringent upper limits on the C iv 1549 angstrom/Ly alpha and He II 1640 angstrom/Ly alpha line ratios, providing a new upper limit on the fraction of active galactic nuclei in Ly alpha selected galaxy samples, and on the contribution of Pop III populations. Finally, we calculate the Ly alpha luminosity function for our z approximate to 4.5 sample, which is consistent with those at other redshifts, showing that there is no evolution in Ly alpha luminosity function from z = 3.1 to 6.6.