Evolution of the Ionizing Background and the Epoch of Reionization from the Spectra of z ∼ 6 Quasars

By Xiaohui Fan, V. Narayanan, M. Strauss, R. White, Robert H. Becker, L. Pentericci, Hans-Walter Rix. 2001

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We study the process of cosmic reionization and estimate the ionizing background in the intergalactic medium (IGM) using the Lyman series absorption in the spectra of the four quasars at 5.7 < z < 6.3 discovered by the Sloan Digital Sky Survey. We derive the redshift evolution of the ionizing background at high redshifts, using both semianalytic techniques and cosmological simulations to model the density fluctuations in the IGM. The existence of the complete Lyα Gunn-Peterson (GP) trough in the spectrum of the z = 6.28 quasar SDSS 1030+0524 indicates a photoionization rate (Γ-12 in units of 10-12 s-1) at z ∼ 6 lower than 0.08, at least a factor of 6 smaller than the value at z ∼ 3. The Lyβ and Lyγ GP troughs give an even stronger limit Γ-12 ≲ 0.02 due to their smaller oscillator strengths, indicating that the ionizing background in the IGM at z ∼ 6 is more than 20 times lower than that at z ∼ 3. Meanwhile, the volume-averaged neutral hydrogen fraction increases from 10-5 at z ∼ 3 to greater than 10-3 at z ∼ 6. At this redshift, the mass-averaged neutral hydrogen fraction is larger than 1%; the mildly overdense regions (δ > 3) are still mostly neutral, and the comoving mean free path of ionizing photons is shorter than 8 Mpc. Comparison with simulations of cosmological reionization shows that the observed properties of the IGM at z ∼ 6 are typical of those in the era at the end of the overlap stage of reionization when the individual H II regions merge. Thus z ∼ 6 marks the end of the reionization epoch. The redshift of reionization constrains the small-scale power of the mass-density fluctuations and the star-forming efficiency of the first generation of objects.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

The VISTA deep extragalactic observations (VIDEO) survey (2012, background): “The SDSS has revolutionized studies of quasi-stellar objects (QSOs) at the highest redshifts (e.g. Fan et al. 2006), providing the first evidence that the epoch of reionization was coming to an end around z 6 (Becker et al. 2001; Fan et al. 2002).”
Line-driven Winds, Ionizing Fluxes, and Ultraviolet Spectra of Hot Stars at Extremely Low Metallicity. I. Very Massive O Stars (2002, result): “…1984; Couchman & Rees 1986; Haiman & Loeb 1997; Bromm, Kudritzki, & Loeb 2001b), which appears to have been reionized at redshifts z possibly larger than 6, as the recent work on quasars (Becker et al. 2001; Djorgovski et al. 2001a; Fan et al. 2000, 2002) and Ly emitters (Hu et al. 2002) indicates.”
NEW CONSTRAINTS ON COSMIC REIONIZATION FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN (2013, background): “However, observations of the Gunn & Peterson (1965) trough in quasar spectra (e.g., Fan et al. 2001, 2002, 2003, 2006b; Djorgovski et al. 2001) indicate that intergalactic gas hasbecome almost fully reionized by redshiftz ∼ 5.”
The Evolution of the Intergalactic Medium Transmission to Redshift 6 (2004, methodology): “And comparison with simulations suggests the IGM could have been fully neutral at z = 6.5 (Cen & McDonald 2002; Fan et al. 2002; Gnedin 2003), though, as we point out in this paper, some of the strongest claims in this regard are based on an incorrect conversion of Ly opacities to equivalent Ly…”
Self-regulated reionization (2006, methodology): “…help explain why the CMB polarization experiments indicate that reionization was well advanced byz >∼ 11 (Spergel & et al. 2006), while quasar absorption spectra suggest that reionization ended later, atz ∼ 6.5 (e.g. Fan et al. 2002; White et al. 2003), implying that the EOR was extended in time.”
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).”
Resolving the Formation of Protogalaxies. II. Central Gravitational Collapse (2007, background): “In addition, supermassive black holes (SMBHs) more massive than 108M are present at these redshifts (e.g., Becker et al. 2001; Fan et al. 2002, 2006).”
Probing reionization with Lyman α emission lines (2003, background): “Limits from QSO spectra at redshifts approaching 6.5 indicate that xH I > 10−3 averaged over the volume of the IGM, and xH I > 10−2 averaged over the mass of the IGM (Fan et al. 2002).”
The 2dF Galaxy Redshift Survey: The Amplitudes of fluctuations in the 2dFGRS and the CMB, and implications for galaxy biasing (2001, background): “Recent important constraints come from the spectra of SDSS quasars, suggesting τ > ∼ 0.03− 0.04 (Becker et al. 2001; Fan et al. 2002).”
Reionization of Hydrogen and Helium by Early Stars and Quasars (2002, background): “This wide range satisfies the constraints that overlap of the H ii regions must be achieved by z 6 (Fan et al. 2002) and that the optical depth for electron scattering must be limited to es < 0:18.”
The physics of the intergalactic medium (2007, background): “…a surge of activity in reionization studies following the discovery of high redshift QSOs (z > 6) with spectra indicating a rapid rise in the effective optical depth of the IGM to Lyα photons, hinting that the Epoch of Reionization was being approached (Becker et al., 2001; Fan et al., 2002).”
Resolving the Formation of Protogalaxies. III. Feedback from the First Stars (2007, background): “Observations of luminous quasars powered by supermassive black holes (SMBH) of mass ∼109M⊙ (Becker et al. 2001; Fan et al. 2002, 2006) and low-luminosity galaxies (Hu et al. 2002; Iye et al. 2006; Kashikawa et al. 2006; Bouwens & Illingworth 2006; Stark et al. 2007) at and above redshift 6 indicate…”
Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ∼ 6 Quasars. II. A Sample of 19 Quasars (2005, methodology): “ar X iv :a st ro -p h/ 05 12 08 2v 2 1 9 M ar 2 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 nineteen quasars at 5.74 zem 6.42 discovered in the Sloan Digital Sky Survey.”
A Survey of z > 5.7 Quasars in the Sloan Digital Sky Survey. II. Discovery of Three Additional Quasars at z > 6 (2003, background): “…Pentericci et al. 2002) indicate that the ionizing background is declining rapidly, and the intergalactic medium neutral fraction is rising sharply at z 6, suggesting that we might be close to the epoch of reionization at this redshift (e.g., Fan et al. 2002; Cen &McDonald 2002; Barkana 2002).”
A Direct Precision Measurement of the Intergalactic Lyα Opacity at 2 ≤ z ≤ 4.2 (2007, methodology): “We have used values of Γbkg that were estimated from previous measurements of τeff (Schaye et al. 2003 for the Bolton et al. 2005 points; Fan et al. 2002 for the Meiksin & White 2004 point), which were generally less precise than ours and to which no continuum corrections were applied.12 Our…”
LOWER-LUMINOSITY GALAXIES COULD REIONIZE THE UNIVERSE: VERY STEEP FAINT-END SLOPES TO THE UV LUMINOSITY FUNCTIONS AT z ⩾ 5–8 FROM THE HUDF09 WFC3/IR OBSERVATIONS (2011, methodology): “Observationally, we have constraints on reionization from the Gunn-Peterson trough in luminous high-redshift quasars (Fan et al. 2002), the Thomson optical depths observed in the Microwave background radiation (Komatsu et al. 2011), and the luminosity function and clustering properties of Lyα…”
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…”
Resolved Molecular Gas in a Quasar Host Galaxy at Redshift z = 6.42 (2004, background): “More and more objects have been found at the highest redshifts in recent years, back to the ’Dark Ages’ (the epoch of formation of the first luminous structures), at z>6 when the universe was less than a gigayear old (e.g., Fan et al. 2002, 2003, 2004, Hu et al. 2002, Stanway et al. 2003).”