AN ATLAS OFz= 5.7 ANDz= 6.5 Lyα EMITTERS,

Abstract

We present an atlas of 88 z~5.7 and 30 z~6.5 Ly alpha emitters obtained from a wide-field narrowband survey. We combined deep narrowband imaging in 120A bandpass filters centered at 8150A and 9140A with deep BVRIz broadband imaging to select high-redshift galaxy candidates over an area of 4180 square arcmin. The goal was to obtain a uniform selection of comparable depth over the 7 targeted fields in the two filters. For the GOODS-N region of the HDF-N field, we also selected candidates using a 120A filter centered at 9210A. We made spectroscopic observations with Keck DEIMOS of nearly all the candidates to obtain the final sample of Ly alpha emitters. At the 3.3A resolution of the DEIMOS observations the asymmetric profile for Ly alpha emission with its steep blue fall-off can be clearly seen in the spectra of nearly all the galaxies. We show that the spectral profiles are surprisingly similar for many of the galaxies and that the composite spectral profiles are nearly identical at z=5.7 and z=6.5. We analyze the distributions of line widths and Ly alpha equivalent widths and find that the lines are marginally narrower at the higher redshift, with median values of 0.77A at z=6.5 and 0.92A at z=5.7. The line widths have a dependence on the Ly alpha luminosity of the form L(L alpha)^(0.3). We compare the surface densities and the luminosity functions at the two redshifts and find that there is a multiplicative factor of 2 decrease in the number density of bright Ly alpha emitters from z=5.7 to z=6.5, while the characteristic luminosity is unchanged.