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arXiv · 1311.0057

Spectroscopy of z ~ 7 candidate galaxies: Using Lyman-alpha to constrain the neutral fraction of hydrogen in the high-redshift universe

Joseph Caruana·Andrew J. Bunker·Stephen M. Wilkins·Elizabeth R. Stanway·Silvio Lorenzoni·Matt J. Jarvis·Holly Elbert
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Abstract

Following our previous spectroscopic observations of $z>7$ galaxies with Gemini/GNIRS and VLT/XSHOOTER, which targeted a total of 8 objects, we present here our results from a deeper and larger VLT/FORS2 spectroscopic sample of Wide Field Camera 3 selected $z>7$ candidate galaxies. With our FORS2 setup we cover the 737-1070nm wavelength range, enabling a search for Lyman-$α$ in the redshift range spanning 5.06 - 7.80. We target 22 $z$-band dropouts and find no evidence of Lyman-$α$ emission, with the exception of a tentative detection ($<5σ$, which is our adopted criterion for a secure detection) for one object. The upper limits on Lyman-$α$ flux and the broad-band magnitudes are used to constrain the rest-frame Equivalent Widths for this line emission. We analyse our FORS2 observations in combination with our previous GNIRS and XSHOOTER observations, and suggest that a simple model where the fraction of high rest-frame Equivalent Width emitters follows the trend seen at $z=3-6.5$ is inconsistent with our non-detections at $z\sim7.8$ at the 96\% confidence level. This may indicate that a significant neutral HI fraction in the intergalactic medium suppresses Lyman-$α$, with an estimated neutral fraction $χ_{HI}\sim0.5$, in agreement with other estimates.

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Joseph Caruana, Andrew J. Bunker, Stephen M. Wilkins, Elizabeth R. Stanway, Silvio Lorenzoni, Matt J. Jarvis, Holly Elbert. 2014-07-03. Spectroscopy of z ~ 7 candidate galaxies: Using Lyman-alpha to constrain the neutral fraction of hydrogen in the high-redshift universe. https://doi.org/10.1093/mnras%2Fstu1341

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