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Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z 6 Quasars. II. A Sample of 19 QuasarsBased on observations obtained with the Sloan Digital Sky Survey at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration, made possible by the generous financial support of the W. M. Keck Foundation, with the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution, and with the Kitt Peak National Observatory 4 m Mayall Telescope. This paper is dedicated to the memory of John N. Bahcall.

Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z 6... We study the evolution of the ionization state of the intergalactic medium (IGM) at the end of the reionization epoch using moderate-resolution spectra of a sample of 19 quasars at 5.74 < zem < 6.42 discovered in the Sloan Digital Sky Survey. Three methods are used to trace IGM properties: (1) the evolution of the Gunn-Peterson (GP) optical depth in the Ly, Ly, and Ly transitions; (2) the distribution of lengths of dark absorption gaps; and (3) the size of H II regions around luminous quasars. Using this large sample, we find that the evolution of the ionization state of the IGM accelerated at z > 5.7: the GP optical depth evolution changes from (1 + z)4.3 to (1 + z)11, and the average length of dark gaps with > 3.5 increases from <10 to >80 comoving Mpc. The dispersion of IGM properties along different lines of sight also increases rapidly, implying fluctuations by a factor of 4 in the UV background at z > 6, when the mean free path of UV photons is comparable to the correlation length of the star-forming galaxies that are thought to have caused reionization. The mean length of dark gaps shows the most dramatic increase at z 6, as well as the largest line-of-sight variations. We suggest using dark gap statistics as a powerful probe of the ionization state of the IGM at yet higher redshift. The sizes of H II regions around luminous quasars decrease rapidly toward higher redshift, suggesting that the neutral fraction of the IGM has increased by a factor of 10 from z = 5.7 to 6.4, consistent with the value derived from the GP optical depth. The mass-averaged neutral fraction is 1%-4% at z 6.2 based on the GP optical depth and H II region size measurements. The observations suggest that z 6 is the end of the overlapping stage of reionization and are inconsistent with a mostly neutral IGM at z 6, as indicated by the finite length of the dark absorption gaps. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Astronomical Journal IOP Publishing

Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z 6 Quasars. II. A Sample of 19 QuasarsBased on observations obtained with the Sloan Digital Sky Survey at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration, made possible by the generous financial support of the W. M. Keck Foundation, with the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution, and with the Kitt Peak National Observatory 4 m Mayall Telescope. This paper is dedicated to the memory of John N. Bahcall.

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Copyright
Copyright © 2006. The American Astronomical Society. All rights reserved. Printed in U.S.A.
ISSN
0004-6256
eISSN
1538-3881
DOI
10.1086/504836
Publisher site
See Article on Publisher Site

Abstract

We study the evolution of the ionization state of the intergalactic medium (IGM) at the end of the reionization epoch using moderate-resolution spectra of a sample of 19 quasars at 5.74 < zem < 6.42 discovered in the Sloan Digital Sky Survey. Three methods are used to trace IGM properties: (1) the evolution of the Gunn-Peterson (GP) optical depth in the Ly, Ly, and Ly transitions; (2) the distribution of lengths of dark absorption gaps; and (3) the size of H II regions around luminous quasars. Using this large sample, we find that the evolution of the ionization state of the IGM accelerated at z > 5.7: the GP optical depth evolution changes from (1 + z)4.3 to (1 + z)11, and the average length of dark gaps with > 3.5 increases from <10 to >80 comoving Mpc. The dispersion of IGM properties along different lines of sight also increases rapidly, implying fluctuations by a factor of 4 in the UV background at z > 6, when the mean free path of UV photons is comparable to the correlation length of the star-forming galaxies that are thought to have caused reionization. The mean length of dark gaps shows the most dramatic increase at z 6, as well as the largest line-of-sight variations. We suggest using dark gap statistics as a powerful probe of the ionization state of the IGM at yet higher redshift. The sizes of H II regions around luminous quasars decrease rapidly toward higher redshift, suggesting that the neutral fraction of the IGM has increased by a factor of 10 from z = 5.7 to 6.4, consistent with the value derived from the GP optical depth. The mass-averaged neutral fraction is 1%-4% at z 6.2 based on the GP optical depth and H II region size measurements. The observations suggest that z 6 is the end of the overlapping stage of reionization and are inconsistent with a mostly neutral IGM at z 6, as indicated by the finite length of the dark absorption gaps.

Journal

The Astronomical Journal – IOP Publishing

Published: Jul 1, 2006

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