Texas Spectroscopic Search for Ly$alpha$ Emission at the End of Reionization III. the Ly$alpha$ Equivalent-width Distribution and Ionized Structures at $z > 7$. (arXiv:2009.10092v2 [astro-ph.GA] UPDATED)

Texas Spectroscopic Search for Ly$alpha$ Emission at the End of Reionization III. the Ly$alpha$ Equivalent-width Distribution and Ionized Structures at $z > 7$. (arXiv:2009.10092v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Jung_I/0/1/0/all/0/1">Intae Jung</a> (1,2,3), <a href="http://arxiv.org/find/astro-ph/1/au:+Finkelstein_S/0/1/0/all/0/1">Steven L. Finkelstein</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Dickinson_M/0/1/0/all/0/1">Mark Dickinson</a> (4), <a href="http://arxiv.org/find/astro-ph/1/au:+Hutchison_T/0/1/0/all/0/1">Taylor A. Hutchison</a> (5), <a href="http://arxiv.org/find/astro-ph/1/au:+Larson_R/0/1/0/all/0/1">Rebecca L. Larson</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Papovich_C/0/1/0/all/0/1">Casey Papovich</a> (5), <a href="http://arxiv.org/find/astro-ph/1/au:+Pentericci_L/0/1/0/all/0/1">Laura Pentericci</a> (6), <a href="http://arxiv.org/find/astro-ph/1/au:+Straughn_A/0/1/0/all/0/1">Amber N. Straughn</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Guo_Y/0/1/0/all/0/1">Yicheng Guo</a> (7), <a href="http://arxiv.org/find/astro-ph/1/au:+Malhotra_S/0/1/0/all/0/1">Sangeeta Malhotra</a> (1,8), <a href="http://arxiv.org/find/astro-ph/1/au:+Rhoads_J/0/1/0/all/0/1">James Rhoads</a> (1,8), <a href="http://arxiv.org/find/astro-ph/1/au:+Song_M/0/1/0/all/0/1">Mimi Song</a> (9), <a href="http://arxiv.org/find/astro-ph/1/au:+Tilvi_V/0/1/0/all/0/1">Vithal Tilvi</a> (8), <a href="http://arxiv.org/find/astro-ph/1/au:+Wold_I/0/1/0/all/0/1">Isak Wold</a> (1) ((1) NASA GSFC, (2) CUA, (3) UT Austin, (4) NOIRLab, (5) Texas A and M Univ., (6) INAF, (7) Univ. of Missouri, (8) Arizona State Univ., (9) Univ. of Massachusetts)

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 ($>$50r{A}), and additional tentative Ly$alpha$
emission lines detected at 3 – 4$sigma$ from five additional galaxies. We
constrain the Ly$alpha$ EW distribution at $zsim7.6$, finding a significant
drop from $zlesssim6$, suggesting an increasing fraction of neutral hydrogen
(HI) in the IGM in this epoch. We estimate the Ly$alpha$ transmission through
the IGM ($=$EW$_{zsimtext{7.6}}$/EW$_{zsimtext{2-6}}$), and infer an IGM HI
fraction ($X_{text{HI}}$) of $49^{+19}_{-19}%$ at $zsim7.6$, 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 $zsim7.55$ 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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