Texas Spectroscopic Search for Lyα Emission at the End of Reionization II. The Deepest Near-Infrared Spectroscopic Observation at z7
Abstract
Realizing the utility of Lyα emission to trace the evolution of the intergalactic medium (IGM) during the epoch of reionization requires deep spectroscopy across the boundary of optical and near-infrared (NIR) spectrographs at z7.2 when Lyα emission is at 1μm. Our Texas Spectroscopic Search for Lyα Emission at the End of Reionization includes 18 nights of deep spectroscopic observations using the Keck DEIMOS (optical) and MOSFIRE (NIR) spectrographs. Within this dataset we observe Lyα emission from 183 photometric-redshift selected galaxies at z = 5.5 - 8.3 from the Cosmic Assembly Near infrared Deep Extragalactic Legacy Survey (CANDELS). Our overlapping MOSFIRE observations, over 84 galaxies total, provide the deepest NIR spectroscopic data yet obtained for Lyα from galaxies z > 7, with >16 hr integration time for four observed galaxies. Here we analyze these four targets, and we report the discovery of a new z = 7.60 Lyα detection as well as provide an updated observation of the previously confirmed z=7.51 Lyα emission from Finkelstein et al. (2013) with a 3× longer exposure time. Our analysis of these Lyα emission line profiles reveal a significant asymmetric shape. The two detected Lyα emission lines from bright sources (MUV<-20.25) could imply that these bright galaxies inhabit ionized bubbles in a partially neutral IGM, although deeper exposures may yet reveal Lyα emission in the fainter sources.