Evidence of patchy hydrogen reionization from an extreme Lyα trough below redshift six

By George D. Becker, J. Bolton, P. Madau, M. Pettini, E. Ryan-Weber, B. Venemans. 2014

316 citations recorded by the source corpus.

We report the discovery of an extremely long (∼110 Mpc/h) and dark (τeff≳7) Lyα trough extending down to z≃5.5 towards the zem≃6.0 quasar ULAS J0148+0600. We use these new data in combination with Lyα forest measurements from 42 quasars at 4.5≤zem≤6.4 to conduct an updated analysis of the line-of-sight variance in the intergalactic Lyα opacity over 4≤z≤6. We find that the scatter in transmission among lines of sight near z∼6 significantly exceeds theoretical expectations for either a uniform ultraviolet background (UVB) or simple fluctuating UVB models in which the mean free path to ionizing photons is spatially invariant. The data, particularly near z≃5.6-5.8, instead require fluctuations in the volume-weighted hydrogen neutral fraction that are a factor of 3 or more beyond those expected from density variations alone. We argue that these fluctuations are most likely driven by large-scale variations in the mean free path, consistent with expectations for the final stages of inhomogeneous hydrogen reionization. Even by z≃5.6, however, a large fraction of the data are consistent with a uniform UVB, and by z∼5 the data are fully consistent with opacity fluctuations arising solely from the density field. This suggests that while reionization may be ongoing at z∼6, it has fully completed by z∼5.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/ee447d8476e65a7c989b5c1f97bcfa3f6675721a

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Citations in the corpus

New constraints on lyman-α opacity with a sample of 62 quasars at z > 5.7 (2018, methodology): “Similarly, Becker et al. (2015b) published spectra of seven quasars, at 5.98 < z < 6.25, not included in a previous work by Fan et al. (2006), obtained on the ESI on the Keck II telescope (Sheinis et al. 2002), and X-Shooter on the Very Large Telescope (VLT).”
The Neutral Hydrogen Cosmological Mass Density at z = 5 (2015, background): “While the bulk of reionization is thought to occur at z > 6, large neutral regions may persist to lower redshifts (e.g. Becker et al. 2015).”
Evolution of the AGN UV luminosity function from redshift 7.5 (2018, background): “Finally, AGN may also provide a natural explanation for the large scatter in the Lyα opacity between different quasar sightlines close to redshift z = 6 (Becker et al. 2015; Bosman et al. 2018; Eilers et al. 2018).”
Radiation Backgrounds at Cosmic Dawn: X-Rays from Compact Binaries (2016, background): “…absorption in the spectra of distant quasars and of cosmic microwave background (CMB) anisotropies and polarization have pushed forward the timelime of hydrogen reionization (Becker et al. 2015; Planck Collaboration et al. 2016) and backward that of helium double reionization (Worseck et al. 2014).”
COSMIC REIONIZATION AFTER PLANCK: COULD QUASARS DO IT ALL? (2015, background): “Studies of resonant absorption in the spectra of distant quasars show that, while inhomogeneous hydrogen reionization may still be ongoing at z ∼ 6, it has fully completed by redshift 5 (e.g., Becker et al. 2015; McGreer et al. 2015; Fan et al. 2006).”
THE PAN-STARRS1 DISTANT z > 5.6 QUASAR SURVEY: MORE THAN 100 QUASARS WITHIN THE FIRST GYR OF THE UNIVERSE (2016, background): “Quasars within the first gigayear of the universe place strong constraints on black hole formation models (Volonteri 2012) and are fundamental probes of the final phases of cosmological reionization (see Becker et al. 2015a; Mortlock 2015, for recent reviews).”
THE EVOLUTION OF THE GALAXY REST-FRAME ULTRAVIOLET LUMINOSITY FUNCTION OVER THE FIRST TWO BILLION YEARS (2014, unknown): “Analyses of the IGM via line-of-sight quasar observations have been able to show that reionization was likely complete by z ~ 6 (e.g., Fan et al. 2006; although see Mesinger 2010 and Becker et al. 2015).”
CONTRASTING GALAXY FORMATION FROM QUANTUM WAVE DARK MATTER, ψDM, WITH ΛCDM, USING PLANCK AND HUBBLE DATA (2015, background): “Beyond which evidence of a patchy opacity is claimed in some QSO and GRB spectra (Chornock et al. 2014; Becker et al. 2015; Melandri et al. 2015) with a small mean enhancement in the average neutral fraction by =z 6.5 (Hartoog et al. 2014).”
New Constraints on the free-streaming of warm dark matter from intermediate and small scale Lyman-$\alpha$ forest data (2017, background): “As discussed in [25] spatial variations in the IGM temperature [37], mean free path [38] and fluctuations from bright Lyman break galaxies at high redshift [39] (particularly at z > 5) may also have an uncertain impact on the flux power.”
Consistent modelling of the meta-galactic UV background and the thermal/ionization history of the intergalactic medium (2018, background): “…studies of Lyman-α absorption in the spectra of distant quasars showed that hydrogen is fully ionized at least out to z ' 5.6, while inhomogeneous reionization may be still ongoing at slightly earlier times, z ' 6 (e.g., Fan et al. 2006; Songaila 2004; Becker et al. 2015; McGreer et al. 2015).”
Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionization (2016, background): “Furthermore, recent findings of significant Lyα opacity fluctuations on large scales in absorption spectra of 5<∼ z <∼ 6 QSOs (Becker et al. 2015) and the observed rapid evolution of Lyα emitters at z > 6 (Ono et al. 2012; Caruana et al. 2014; Schenker et al. 2014; Pentericci et al. 2014; Tilvi et…”
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).”
Physical Properties of 15 Quasars at z ≳ 6.5 (2017, unknown): “…the evolution of the IGM ionized fraction during the EoR through high−z quasar emission, e.g. by measuring transmission spikes in the Lyα forest (e.g., Fan et al. 2006, Becker et al. 2015, Barnett et al. 2017), and by computing the Lyα power spectrum (e.g., PalanqueDelabrouille et al. 2013).”
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): “Becker et al. (2015) showed that the dispersion in τeff at these redshifts is significantly larger than that expected from density fluctuations alone (Lidz et al. 2006, 2007; Mesinger 2010).”
Conditions for Reionizing the Universe with a Low Galaxy Ionizing Photon Escape Fraction (2019, background): “N 10 0.58551˙ ) was derived assuming that the ionizing background is uniform, while recent measurements imply that there are substantial spatial variations (e.g., Fan et al. 2006; Becker et al. 2015, 2018; Bosman et al. 2018).”
THE FINAL SDSS HIGH-REDSHIFT QUASAR SAMPLE OF 52 QUASARS AT z > 5.7 (2016, background): “The spectrum of J0841+2905 was obtained from the MMT. Note that there exist higher S/N optical spectra for some quasars (e.g., Becker et al. 2011, 2015) that are not shown in Figure 12.”
Inferring the astrophysics of reionization and cosmic dawn from galaxy luminosity functions and the 21-cm signal (2018, methodology): “These authors estimated the ionizing emissivity at 4.8 < z < 5.8 based on the measurement of τLyα by Becker et al. (2015).”
Cosmic Dawn (CoDa): the first radiation-hydrodynamics simulation of reionization and galaxy formation in the Local Universe (2015, background): “…al. 2006), further quasar Lyman α observations have shown that extended opaque hydrogen troughs may still exist below this redshift, highlighting the patchiness of the process and suggesting that the reionization may actually still be ongoing at z = 6 and end as low as z ∼ 5 Becker et al. (2015).”