LYMAN BREAK GALAXIES AT z ∼ 5: REST-FRAME UV SPECTRA. III

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 (MUV < -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 Lyα equivalent widths was reinforced. We discuss possible causes for the deficiency and prefer the interpretation of dust absorption.