Evidence for Reionization at z ∼ 6: Detection of a Gunn-Peterson Trough in a z = 6.28 Quasar

By Robert H. Becker, Xiaohui Fan, R. White, M. Strauss, V. Narayanan, Robert Lupton, James E. Gunn, James Annis, N. Bahcall, J. Brinkmann and 20 more. 2001

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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.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR (2020, background): “Observations of the Gunn-Peterson trough in highredshift quasar spectra (e.g. Becker et al. 2001; Fan et al. 2006) and the measurement of the optical depth to Thomson scattering of the Cosmic Microwave Background (CMB) radiation (e.g. Planck Collaboration et al. 2016b) both suggest that the bulk of…”
Wide-Field InfrarRed Survey Telescope-Astrophysics Focused Telescope Assets WFIRST-AFTA 2015 Report (2015, background): “…black holes a mere few hundred million years after the Big Bang, and whose light can potentially illuminate the transition of intergalactic gas in the universe from neutral to an ionized phase (GunnPeterson effect Gunn & Peterson 1965, Becker et al. 2001, Djorgovski et al. 2001, Fan et al. 2003).”
The Evolution of the Intergalactic Medium (2015, background): “…forests cannot be used to directly detect neutral regions,19 the z > 5 Lymanseries forest exhibits dramatic evolution in the mean opacity as well as extremely large spatial fluctuations in the transmission (Becker et al. 2001; Fan et al. 2002, 2006; Mortlock et al. 2011; Becker et al. 2015).”
REIONIZATION AFTER PLANCK: THE DERIVED GROWTH OF THE COSMIC IONIZING EMISSIVITY NOW MATCHES THE GROWTH OF THE GALAXY UV LUMINOSITY DENSITY (2015, background): “The most important constraints make use of the Gunn–Peterson optical depth measured from bright z ∼ 6 quasars (Becker et al. 2001; Fan et al. 2006a, 2006b) and also by looking at the distribution of dark gaps in z = 6 quasar spectra (McGreer et al. 2015) which suggest that cosmic reionization is…”
Mapping Neutral Hydrogen during Reionization with the Lyα Emission from Quasar Ionization Fronts (2007, positive): “At z k 6, quasar spectra start showing complete Gunn-Peterson (1965) absorption troughs (GPTs), which might suggest a rapid increase in the neutral fraction of cosmic hydrogen (Becker et al. 2001; Fan et al. 2003; White et al. 2003).”
SEGUE: A SPECTROSCOPIC SURVEY OF 240,000 STARS WITH g = 14–20 (2009, background): “The major science program consists of constructing a large three-dimensional map of the universe and constraining cosmological models; see, e.g. Becker et al. (2001); Blanton et al. (2003b); Fan et al. (2003); Tremonti et al. (2004); Tegmark et al. (2004); Eisenstein et al. (2005); Richards et al.…”
ON THE STELLAR POPULATIONS AND EVOLUTION OF STAR-FORMING GALAXIES AT 6.3 < z ⩽ 8.6 (2009, background): “JOINT CONSTRAINTS ON COSMIC REIONIZATION AND GALAXY PROPERTIES The presence of galaxies atz∼ 7 andz∼ 8 allows us to test how these galaxies contribute to cosmic reionization, which is believed to be in progress during this time (e.g., Becker et al. 2001; Fan et al. 2006; Dunkley et al. 2009).”
THE STELLAR MASS DENSITY AND SPECIFIC STAR FORMATION RATE OF THE UNIVERSE AT z ∼ 7 (2009, background): “From absorption studies to bright z ∼ 6 QSOs, the process of reionizing the hydrogen of the universe was just ending at z ∼ 6 (Fan et al. 2006; Becker et al. 2001) while the five year WMAP results suggest it began at least as early as z ∼ 11 (Komatsu et al. 2009).”
Foreground simulations for the LOFAR-epoch of reionization experiment (2008, background): “…the sudden jump in the Lyα optical depth in the Gunn–Peterson troughs (Gunn & Peterson 1965) observed in the Sloan Digital Sky Survey quasar spectra (Becker et al. 2001; Fan et al. 2001; Pentericci et al. 2002; White et al. 2003; Fan et al. 2006), marking a lower limit to the redshift at which…”
Luminosity Functions of Lyα Emitters at Redshifts z = 6.5 and z = 5.7: Evidence against Reionization at z ≤ 6.5 (2004, background): “INTRODUCTION While the observations of quasars show a Gunn-z 1 6 Peterson trough, implying a neutral intergalactic medium (IGM) at (Becker et al. 2001; Fan et al. 2002; but cf.z ≈ 6 Songaila & Cowie 2002), microwave background observations imply substantial ionization at (Spergel et al. 2003;z 15…”
Lyα Emitting Galaxies as a Probe of Reionisation (2014, background): “Gunn-Peterson troughs that have been detected in the spectra of quasars z 6 (e.g. Becker et al. 2001; Fan et al. 2002; Mortlock et al. 2011; Venemans et al. 2013) suggest that the intergalactic medium (IGM) contained a significant neutral fraction (with a volume averaged fraction 〈xHI〉V ∼ 0.1, see…”
The contribution of high-redshift galaxies to cosmic reionization: New results from deep WFC3 imaging of the Hubble Ultra Deep Field (2009, methodology): “The GunnPeterson trough was first discovered in the spectra of SDSS quasars (Becker et al. 2001, Fan et al. 2001, 2006).”
Photoevaporation of cosmological minihaloes during reionization (2003, background): “The detection of GP troughs in the spectra of Sloan Digital Sky Survey (SDSS) quasars at z 6 places a lower limit on the mean H I density in the IGM at z = 6 large enough to suggest that reionization might only just have ended at z ≈ 6 (Becker et al. 2001; Djorgovski et al. 2001; Fan et al. 2003).”
The Hubble Ultra Deep Field (2003, methodology): “The first observation of this epoch came with detection of the Gunn-Peterson hydrogen edge in the spectra of distant quasars discovered in the Sloan Digital Sky Survey (Becker et al. 2001, Fan et al. 2002), putting the redshift of complete reionization around 6.”
The morphology of H ii regions during reionization (2006, background): “Observations of high-redshift quasars, gamma-ray bursts and Lyα emitters are currently probing redshifts at which the Universe may have been significantly neutral (Becker et al. 2001; White et al. 2003; Santos et al. 2004; Fan et al. 2006; Kashikawa 2006; Totani et al. 2006).”