Ly-alpha emitting galaxies at redshift z~4.5 in the LALA Cetus field

TL;DR

This paper reports a large spectroscopic sample of Ly-alpha emitting galaxies at redshift 4.5, revealing a significant density drop possibly due to a large-scale void, and provides new constraints on galaxy properties and evolution at this epoch.

Contribution

It presents the largest spectroscopic confirmation of z~4.5 Ly-alpha emitters, analyzes their distribution, and constrains the Ly-alpha luminosity function and galaxy properties at this redshift.

Findings

Detected 110 Ly-alpha emitters at z~4.5.

Found a 66% drop in LAE density indicating a possible large-scale void.

Established that the Ly-alpha luminosity function shows no evolution from z~3.1 to 6.6.

Abstract

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.