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arXiv · 1011.5313

Ly alpha emissters at z=6.5 in the SSA22 field: An area more neutral or void at the end of the reionization epoch

E. Nakamura·A. K. Inoue·T. Hayashino·M. Horie·K. Kousai·T. Fujii·Y. Matsuda
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Abstract

We present results of a survey of Lyman $α$ emitters (LAEs) at $z=6.5$ which is thought to be the final epoch of the cosmic reionization. In a $\approx530$ arcmin$^2$ deep image of the SSA22 field taken through a narrowband filter NB912 installed in the Subaru/Suprime-Cam, we have found only 14 LAE candidates with $L_{\rm Lyα}\ga3\times10^{42}$ erg s$^{-1}$. Even applying the same colour selection criteria, the number density of the LAE candidates is a factor of 3 smaller than that found at the same redshift in the Subaru Deep field (SDF). Assuming the number density in the SDF is a cosmic average, the probability to have a number density equal to or smaller than that found in the SSA22 field is only 7% if we consider fluctuation by the large-scale structure (i.e. cosmic variance) and Poisson error. Therefore, the SSA22 field may be a rare void at $z=6.5$. On the other hand, we have found that the number density of $i'$-drop galaxies with $25.5<z'<26.0$ in the SSA22 field agrees well with that in the SDF. If we consider a scenario that a larger neutral fraction of intergalactic hydrogen, $x_{\rm HI}$, in the SSA22 field obscures a part of Ly$α$ emission, $x_{\rm HI}$ in the SSA22 field should be about 2 times larger than that in the SDF. This can be translated into $x_{\rm HI}<0.9$ at $z=6.5$ in the SSA22 field. A much larger survey area than previous ones is required to overcome a large fluctuation reported here and to obtain a robust constraint on $x_{\rm HI}$ at the end of the reionization from LAEs.

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E. Nakamura, A. K. Inoue, T. Hayashino, M. Horie, K. Kousai, T. Fujii, Y. Matsuda. 2010-11-24. Ly alpha emissters at z=6.5 in the SSA22 field: An area more neutral or void at the end of the reionization epoch. https://doi.org/10.1111/j.1365-2966.2010.18077.x

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