Texas Spectroscopic Search for Ly Emission at the End of Reionization. III. The Ly Equivalent-width Distribution and Ionized Structures at z > 7
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AbstractLy emission from galaxies can be utilized to characterize the ionization state in the intergalactic medium (IGM). We report our search for Ly emission at z>7 using a comprehensive Keck/MOSFIRE near-infrared spectroscopic data set, as part of the Texas Spectroscopic Search for Ly 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 4.519 hr. Utilizing an improved automated emission-line search, we report 10 Ly emission lines detected (>4) at z>7, significantly increasing the spectroscopically confirmed sample. Our sample includes large equivalent-width (EW) Ly emitters (>50 ), and additional tentative Ly emission lines detected at 34 from five additional galaxies. We constrain the Ly EW distribution at z7.6, finding a significant drop from z6, suggesting an increasing fraction of neutral hydrogen (H i) in the IGM in this epoch. We estimate the Ly transmission through the IGM (=EWz7.6/EW) and infer an IGM H i fraction (XHI) of m{ \% }}$?> at z7.6, which is lower in modest tension (>1) with recent measurements at z 7.6. The spatial distribution of the detected Ly emitters implies the presence of a potential highly ionized region at z7.55, which hosts four Ly emitters within a 40 cMpc spatial separation. The prominence of this ionized region in our data set could explain our lower inferred value of XHI, though our analysis is also sensitive to the chosen reference Ly EW distribution values and reionization models.
