Journal Article

Lyα emitters at <i>z</i>= 6.5 in the SSA22 field: an area more neutral or void at the end of the re-ionization epoch*

E. Nakamura, A. K. Inoue, T. Hayashino, M. Horie, K. Kousai, T. Fujii and Y. Matsuda

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 412, issue 4, pages 2579-2586
Published in print April 2011 | ISSN: 0035-8711
Published online April 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.18077.x
Lyα emitters at z= 6.5 in the SSA22 field: an area more neutral or void at the end of the re-ionization epoch*

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We present results of a survey of Lyα emitters (LAEs) at z= 6.5 which is thought to be the final epoch of the cosmic re-ionization. In a ≈530 arcmin2 deep image of the SSA22 field taken through a narrow-band filter NB912 installed in the Subaru/Suprime-Cam, we have found only 14 LAE candidates with LLyα≳ 3 × 1042 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 per cent 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, xH I, in the SSA22 field obscures a part of Lyα emission, xH I in the SSA22 field should be about two times larger than that in the SDF. This can be translated into xH I < 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 xH I at the end of the re-ionization from LAEs.

Keywords: galaxies: high-redshift; intergalactic medium; cosmology: observations

Journal Article.  5950 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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