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Title:
Evidence for Reionization at z~6: Detection of a Gunn-Peterson Trough in a z=6.28 Quasar
Authors:
Becker, Robert H.; Fan, Xiaohui; White, Richard L.; Strauss, Michael A.; Narayanan, Vijay K.; Lupton, Robert H.; Gunn, James E.; Annis, James; Bahcall, Neta A.; Brinkmann, J.; Connolly, A. J.; Csabai, István; Czarapata, Paul C.; Doi, Mamoru; Heckman, Timothy M.; Hennessy, G. S.; Ivezić, Željko; Knapp, G. R.; Lamb, Don Q.; McKay, Timothy A.; Munn, Jeffrey A.; Nash, Thomas; Nichol, Robert; Pier, Jeffrey R.; Richards, Gordon T.; Schneider, Donald P.; Stoughton, Chris; Szalay, Alexander S.; Thakar, Aniruddha R.; York, D. G.
Affiliation:
AA(Department of Physics, University of California at Davis, Davis, CA 95616; IGPP/Lawrence Livermore National Laboratory, Livermore, CA 94550.), AB(Institute for Advanced Study, Olden Lane, Princeton, NJ 08540.), AC(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218.), AD(Princeton University Observatory, Princeton, NJ 08544.), AE(Princeton University Observatory, Princeton, NJ 08544.), AF(Princeton University Observatory, Princeton, NJ 08544.), AG(Princeton University Observatory, Princeton, NJ 08544.), AH(Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510.), AI(Princeton University Observatory, Princeton, NJ 08544.), AJ(Apache Point Observatory, P.O. Box 49, Sunspot, NM 88349.), AK(Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260.), AL(Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218; Department of Physics of Complex Systems, Eötvös University, H-1117 Budapest, Hungary.), AM(Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510.), AN(Department of Astronomy and Research Center for the Early Universe, School of Science, University of Tokyo, Hongo, Bunkyo, Tokyo 113-0033, Japan.), AO(Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218.), AP(US Naval Observatory, 3450 Massachusetts Avenue, NW, Washington, DC 20392-5420.), AQ(Princeton University Observatory, Princeton, NJ 08544.), AR(Princeton University Observatory, Princeton, NJ 08544.), AS(Astronomy and Astrophysics Center, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637.), AT(Department of Physics, University of Michigan, 500 East University, Ann Arbor, MI 48109.), AU(US Naval Observatory, Flagstaff Station, P.O. Box 1149, Flagstaff, AZ 86002-1149.), AV(Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510.), AW(Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15232.), AX(US Naval Observatory, Flagstaff Station, P.O. Box 1149, Flagstaff, AZ 86002-1149.), AY(Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802.), AZ(Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802.), BA(Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510.), BB(Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218.), BC(Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218.), BD(Astronomy and Astrophysics Center, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637; Enrico Fermi Institute, 5640 South Ellis Avenue, Chicago, IL 60637.)
Publication:
The Astronomical Journal, Volume 122, Issue 6, pp. 2850-2857. (AJ Homepage)
Publication Date:
12/2001
Origin:
UCP
Astronomy Keywords:
Cosmology: Observations, Galaxies: Formation, Galaxies: Quasars: Absorption Lines, Galaxies: Quasars: General
DOI:
10.1086/324231
Bibliographic Code:
2001AJ....122.2850B

Abstract

We present moderate-resolution Keck spectroscopy of quasars at z=5.82, 5.99, and 6.28, discovered by the Sloan Digital Sky Survey (SDSS). We find that the Lyα absorption in the spectra of these quasars evolves strongly with redshift. To z~5.7, the Lyα absorption evolves as expected from an extrapolation from lower redshifts. However, in the highest-redshift object, SDSSp J103027.10+052455.0 (z=6.28), the average transmitted flux is 0.0038+/-0.0026 times that of the continuum level over 8450 Å<λ<8710 Å (5.95<zabs<6.16), consistent with zero flux. Thus the flux level drops by a factor of greater than 150 and is consistent with zero flux in the Lyα forest region immediately blueward of the Lyα emission line, compared with a drop by a factor of ~10 at zabs~5.3. A similar break is seen at Lyβ because of the decreased oscillator strength of this transition, this allows us to put a considerably stronger limit, τeff>20, on the optical depth to Lyα absorption at z=6. This is a clear detection of a complete Gunn-Peterson trough, caused by neutral hydrogen in the intergalactic medium. Even a small neutral hydrogen fraction in the intergalactic medium would result in an undetectable flux in the Lyα forest region. Therefore, the existence of the Gunn-Peterson trough by itself does not indicate that the quasar is observed prior to the reionization epoch. However, the fast evolution of the mean absorption in these high-redshift quasars suggests that the mean ionizing background along the line of sight to this quasar has declined significantly from z~5 to 6, and the universe is approaching the reionization epoch at z~6. Based on observations obtained 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, and with the Sloan Digital Sky Survey, which is owned and operated by the Astrophysical Research Consortium.
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