Ly-alpha emitting galaxies at redshift z~4.5 in the LALA Cetus field
  We present a large sample of Ly-alpha emitting galaxies spectroscopically
confirmed at z~4.5, based on IMACS spectroscopic observations of candidate LAEs
in the LALA Cetus field. We identify 110 z~4.5 LAEs based on single line
detections with no continuum emission blueward of the line. 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 4.39-4.47 by a factor of 66%,
which could be a large scale void in the distribution of star-forming galaxies
(~18Mpc along the line of sight and ~80Mpc across). The sample includes many
objects with equivalent widths >200A. 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 CIV 1549/Ly-alpha and HeII 1640/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~4.5 sample, which is
consistent with those at other redshifts, showing that there is no evolution in
Ly-alpha luminosity function from z~3.1-6.6.
