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Evidence for Reionization at z ~ 6: Detection of a Gunn-Peterson Trough in a z=6.28 Quasar | | Robert H. Becker
; Xiaohui Fan
; Richard L. White
; Michael A. Strauss
; Vijay K. Narayanan
; Robert H. Lupton
; James E. Gunn
; James Annis
; Neta A. Bahcall
; J. Brinkmann
; A. J. Connolly
; Istvan Csabai
; Paul C. Czarapata
; Mamoru Doi
; Timothy M. Heckman
; G. S. Hennessy
; Zeljko Ivezic
; G. R. Knapp
; Don Q. Lamb
; Timothy A. McKay
; Jeffrey A. Munn
; Thomas Nash
; Robert Nichol
; Jeffrey R. Pier
; Gordon T. Richards
; Donald P. Schneider
; Chris Stoughton
; Alexander S. Szalay
; Anirudda R. Thakar
; D. G. York
; | | Date: |
6 Aug 2001 | | Journal: | Astron.J. 122 (2001) 2850 | | Subject: | astro-ph | | 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 Ly Alpha absorption in the spectra of these quasars evolves strongly with redshift. To z~5.7, the Ly Alpha 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 A < lambda < 8710 A (5.95150, and is consistent with zero flux in the Ly Alpha forest region immediately blueward of the Ly Alpha emission line, compared with a drop by a factor of ~10 at z(abs)~5.3. A similar break is seen at Ly Beta; because of the decreased oscillator strength of this transition, this allows us to put a considerably stronger limit, tau(eff) > 20, on the optical depth to Ly Alpha 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 Ly Alpha 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. | | Source: | arXiv, astro-ph/0108097 | | Services: | Forum | Review | PDF | Favorites | |
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