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arXiv · 2009.10092

Texas Spectroscopic Search for Ly$\alpha$ Emission at the End of Reionization III. the Ly$\alpha$ Equivalent-width Distribution and Ionized Structures at $z > 7$

Intae Jung·Steven L. Finkelstein·Mark Dickinson·Taylor A. Hutchison·Rebecca L. Larson·Casey Papovich·Laura Pentericci·Amber N. Straughn·Yicheng Guo·Sangeeta Malhotra·James Rhoads·Mimi Song·Vithal Tilvi·Isak Wold
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Abstract

Ly$\alpha$ emission from galaxies can be utilized to characterize the ionization state in the intergalactic medium (IGM). We report our search for Ly$\alpha$ emission at $z>7$ using a comprehensive Keck/MOSFIRE near-infrared spectroscopic dataset, as part of the Texas Spectroscopic Search for Ly$\alpha$ 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$\alpha$ emission lines detected ($>$4$\sigma$) at $z>7$, significantly increasing the spectroscopically confirmed sample. Our sample includes large equivalent-width (EW) Ly$\alpha$ emitters ($>$50\r{A}), and additional tentative Ly$\alpha$ emission lines detected at 3 - 4$\sigma$ from five additional galaxies. We constrain the Ly$\alpha$ EW distribution at $z\sim7.6$, finding a significant drop from $z\lesssim6$, suggesting an increasing fraction of neutral hydrogen (HI) in the IGM in this epoch. We estimate the Ly$\alpha$ transmission through the IGM ($=$EW$_{z\sim\text{7.6}}$/EW$_{z\sim\text{2-6}}$), and infer an IGM HI fraction ($X_{\text{HI}}$) of $49^{+19}_{-19}\%$ at $z\sim7.6$, which is lower in modest tension ($>$1$\sigma$) with recent measurements at $z \sim$ 7.6. The spatial distribution of the detected Ly$\alpha$ emitters implies the presence of a potential highly ionized region at $z\sim7.55$ which hosts four Ly$\alpha$ emitters within a $\sim$ 40 cMpc spatial separation. The prominence of this ionized region in our dataset could explain our lower inferred value of $X_{\text{HI}}$, though our analysis is also sensitive to the chosen reference Ly$\alpha$ EW distribution values and reionization models.

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Intae Jung, Steven L. Finkelstein, Mark Dickinson, Taylor A. Hutchison, Rebecca L. Larson, Casey Papovich, Laura Pentericci, Amber N. Straughn, Yicheng Guo, Sangeeta Malhotra, James Rhoads, Mimi Song, Vithal Tilvi, Isak Wold. 2020-09-21. Texas Spectroscopic Search for Ly$\alpha$ Emission at the End of Reionization III. the Ly$\alpha$ Equivalent-width Distribution and Ionized Structures at $z > 7$. https://doi.org/10.3847/1538-4357/abbd44

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