Lyman break galaxies at z ∼ 5: rest-frame UV spectra. III.

Abstract

We present results of optical spectroscopic observations of candidates of Lyman break galaxies (LBGs) at z ∼ 5 in the region, including the GOODS-N and the J0053+1234 regions by using Gemini Multi-Object Spectrograph North and South, respectively. Among 25 candidates, five objects are identified to be at z ∼ 5 (two of them were already identified by an earlier study) and one object very close to the color-selection window turned out to be a foreground galaxy. With this spectroscopically identified sample and those from previous studies, we derived the lower limits on the number density of bright (M[subscript UV] [less than] −22.0 mag) LBGs at z ∼ 5. These lower limits are comparable to or slightly smaller than the number densities of UV luminosity functions (UVLFs) that show the smaller number density among z ∼ 5 UVLFs in literature. However, by considering that there remain many LBG candidates without spectroscopic observations, the number density of bright LBGs is expected to increase by a factor of two or more. The evidence for the deficiency of UV luminous LBGs with large Ly[alpha] equivalent widths was reinforced. We discuss possible causes for the deficiency and prefer the interpretation of dust absorption.