Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ∼ 6 Quasars. II. A Sample of 19 Quasars

By Xiaohui Fan, M. Strauss, Robert H. Becker, R. White, James E. Gunn, G. Knapp, G. T. Richards, D. Schneider, J. Brinkmann, M. Fukugita. 2005

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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 Lyα, Lyβ, and Lyγ 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 τ ∼ (1 + z)4.3 to (1 + z)≳11, and the average length of dark gaps with τ > 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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/25020e7654a50958598640ed5ea9d795e3a46312

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Citations in the corpus

THE SDSS-III BARYON OSCILLATION SPECTROSCOPIC SURVEY: THE QUASAR LUMINOSITY FUNCTION FROM DATA RELEASE NINE (2012, background): “…et al. 2000; Fan et al. 2001; Wolf et al. 2003; Hunt et al. 2004; Fan et al. 2004; Croom et al. 2004; Hao et al. 2005; Richards et al. 2005, 2006b; Fan et al. 2006; Jiang et al. 2006; Fontanot et al. 2007; Bongiorno et al. 2007; Reyes et al. 2008; Jiang et al. 2008, 2009; Croom et al. 2009a;…”
THE CANADA–FRANCE HIGH-z QUASAR SURVEY: NINE NEW QUASARS AND THE LUMINOSITY FUNCTION AT REDSHIFT 6 (2009, methodology): “The most recent published sample from Fan et al. (2006c) contains 14 quasars at 5.74 < z < 6.42 with uniform selection criteria found from a total sky area of ∼6600 deg2.”
21cmfast: a fast, seminumerical simulation of the high‐redshift 21‐cm signal (2010, methodology): “Glimpses of the z ∼ 6–8 Universe were provided by quasars (e.g. Fan et al. 2006), candidate Lyman break galaxies (e.g. Bouwens et al. 2008, 2009; McLure et al. 2009; Ouchi et al. 2009), Lyman alpha emitters (LAEs; e.g. Kashikawa et al. 2006; Shimasaku et al. 2006) and GRBs (e.g. Cusumano et al.…”
A refined measurement of the mean transmitted flux in the Lyα forest over 2 < z < 5 using composite quasar spectra (2012, methodology): “At the highest redshifts (z > 5), F (z) measurements have generally relied on extrapolating a power-law continuum from redward of the Lyα emission line (Songaila 2004; Fan et al. 2006; Becker et al. 2007).”
SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844–7.213: DEMOGRAPHICS OF Lyα EMISSION IN z ∼ 7 GALAXIES (2011, background): “However, investigating the spectra of SDSS quasars, Fan et al. (2006) studied the evolution of the Gunn-Peterson optical depth and demonstrated that the IGM reionization may have ended as late as z ∼ 6.”
Hydrogen Epoch of Reionization Array (HERA) (2016, background): “Lyman-α absorption features in quasar and γ-ray burst spectra give ionization constraints at the tail end of reionization (z < 7, Fan et al. 2006; McGreer et al. 2015), but these features saturate at low neutral fractions xHI & 10−4, where xHI is the fraction of hydrogen in its neutral state.”
ON LYMAN-LIMIT SYSTEMS AND THE EVOLUTION OF THE INTERGALACTIC IONIZING BACKGROUND (2011, background): “If interpreted as a change in Γ, Fan et al. (2006) estimated that a factor of at least 2 change was required over ∆z ≈ 0.5.”
Large Ly α opacity fluctuations and low CMB τ in models of late reionization with large islands of neutral hydrogen extending to z < 5.5 (2018, background): “The effective optical depth (τeff ) of Lyman-α (Lyα) absorption in QSO spectra at redshift z & 5 is observed to exhibit large spatial fluctuations (Fan et al. 2006; Willott et al. 2007; Becker et al. 2015; Barnett et al. 2017; Tang et al. 2017; Bosman et al. 2018; Eilers et al. 2018).”
An updated analytic model for attenuation by the intergalactic medium (2014, methodology): “In particular, the M95 model deviates from the observations at z > 5 because it does not have a rapid increase of the LAF number density towards the epoch of the reionization found in the last decade (e.g. Fan et al. 2006).”
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).”
Ionization state of inter-stellar medium in galaxies: evolution, SFR-M * -Z dependence, and ionizing photon escape (2013, background): “If this correlation of ionization parameter and fesc is established, ionization parameters allow us to investigate ionizing photon escapes that cannot be directly observed for galaxies at the epoch of reionization (z > 6; Fan et al. 2006; Dunkley et al. 2009).”
GeV gamma-ray attenuation and the high-redshift UV background (2009, methodology): “We expect our approach to be reasonably accurate at predicting the ionizing and non-ionizing background fields out to redshift ∼ 6, where H I Gunn-Peterson troughs appear in observed quasar spectra (Fan et al. 2006).”
The Evolution of the Intergalactic Medium (2015, methodology): “…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).”
Faint AGNs at z > 4 in the CANDELS GOODS-S field: looking for contributors to the reionization of the Universe (2015, methodology): “The reionization of the universe, after its neutral phase followed by recombination, appears well completed at z ∼ 6 as inferred from the high ionization level of the intergalactic medium (IGM) observed in the Lyman-α forest of high redshift QSO spectra (Fan et al. (2006)).”