We present a large sample of Ly- \alpha emitting galaxies spectroscopically confirmed at redshift z \approx 4.5 , based on IMACS spectroscopic observations of candidate z \approx 4.5 Ly \alpha -emitting galaxies in the Large Area Lyman Alpha ( LALA ) narrow band imaging survey Cetus field .
We identify 110 of them as z \approx 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 \pm 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 ( \sim 18 Mpc along the line of sight and \sim 80 Mpc across ) .
The sample includes many objects with equivalent widths ( EW ) \gtrsim 200 Å .
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 1549Å / Ly- \alpha and HeII 1640Å / 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 \approx 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 .