TY - JOUR
T1 - Evidence for reionization at z ∼ 6
T2 - Detection of a gunn-peterson trough in a z = 6.28 quasar
AU - Becker, Robert H.
AU - Fan, Xiaohui
AU - White, Richard L.
AU - Strauss, Michael A.
AU - Narayanan, Vijay K.
AU - Lupton, Robert H.
AU - Gunn, James E.
AU - Annis, James
AU - Bahcall, Neta A.
AU - Brinkmann, J.
AU - Connolly, A. J.
AU - Csabai, István
AU - Czarapata, Paul C.
AU - Doi, Mamoru
AU - Heckman, Timothy M.
AU - Hennessy, G. S.
AU - Ivezić, Željko
AU - Knapp, G. R.
AU - Lamb, Don Q.
AU - Mckay, Timothy A.
AU - Munn, Jeffrey A.
AU - Nash, Thomas
AU - Nichol, Robert
AU - Pier, Jeffrey R.
AU - Richards, Gordon T.
AU - Schneider, Donald P.
AU - Stoughton, Chris
AU - Szalay, Alexander S.
AU - Thakar, Aniruddha R.
AU - York, D. G.
PY - 2001/12
Y1 - 2001/12
N2 - 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.
AB - 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.
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U2 - 10.1086/324231
DO - 10.1086/324231
M3 - Article
AN - SCOPUS:0042117667
SN - 0004-6256
VL - 122
SP - 2850
EP - 2857
JO - Astronomical Journal
JF - Astronomical Journal
IS - 6
ER -