Texas Spectroscopic Search for Lyα Emission at the End of Reionization. III. The Lyα Equivalent-width Distribution and Ionized Structures at z > 7

Abstract

Abstract Ly α emission from galaxies can be utilized to characterize the ionization state in the intergalactic medium (IGM). We report our search for Ly α emission at z > 7 using a comprehensive Keck/MOSFIRE near-infrared spectroscopic data set, as part of the Texas Spectroscopic Search for Ly α Emission at the End of Reionization Survey. We analyze data from 10 nights of MOSFIRE observations which together target 72 high- z candidate galaxies in the GOODS-N field, all with deep exposure times of 4.5–19 hr. Utilizing an improved automated emission-line search, we report 10 Ly α emission lines detected (>4 σ ) at z > 7, significantly increasing the spectroscopically confirmed sample. Our sample includes large equivalent-width (EW) Ly α emitters (>50 Å), and additional tentative Ly α emission lines detected at 3 σ –4 σ from five additional galaxies. We constrain the Ly α EW distribution at z ∼ 7.6, finding a significant drop from z ≲ 6, suggesting an increasing fraction of neutral hydrogen (H i ) in the IGM in this epoch. We estimate the Ly α transmission through the IGM (=EW z ∼ 7.6 /EW ) and infer an IGM H i fraction ( X HI ) of at z ∼ 7.6, which is lower in modest tension (>1 σ ) with recent measurements at z ∼ 7.6. The spatial distribution of the detected Ly α emitters implies the presence of a potential highly ionized region at z ∼ 7.55, which hosts four Ly α emitters within a ∼40 cMpc spatial separation. The prominence of this ionized region in our data set could explain our lower inferred value of X HI , though our analysis is also sensitive to the chosen reference Ly α EW distribution values and reionization models.