Model-independent evidence in favour of an end to reionization by z ≈ 6

By I. McGreer, A. Mesinger, V. D’Odorico. 2014

366 citations recorded by the source corpus.

We present new upper limits on the volume-weighted neutral hydrogen fraction, , at z~5-6 derived from spectroscopy of bright quasars. The fraction of the Lyman-alpha and Lyman-beta forests that is "dark" (with zero flux) provides the only model-independent upper limit on , requiring no assumptions about the physical conditions in the intergalactic medium or the quasar's unabsorbed UV continuum. In this work we update our previous results using a larger sample (22 objects) of medium-depth (~ few hours) spectra of high-redshift quasars obtained with the Magellan, MMT, and VLT. This significantly improves the upper bound on derived from dark pixel analysis to <= 0.04 + 0.05 (1{\sigma}) at z=5.6. These results provide robust constraints for theoretical models of reionization, and provide the strongest available evidence that reionization has completed (or is very nearly complete) by z~6.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/d955ed5856d361969d05eaef1bf81e9e517e1035

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In Astronomy and Astrophysics

1. L. Hernquist
2. P. Hopkins
3. M. McQuinn
4. Richard S. Ellis
5. A. Mesinger
6. S. Furlanetto
7. R. Bouwens
8. P. Oesch

In Instrumentation

1. Richard S. Ellis
2. R. Bouwens
3. P. Oesch
4. P. Hopkins
5. L. Hernquist
6. G. Illingworth
7. J. Dunlop
8. C. Conroy

Citations in the corpus

• FIRST SEASON MWA EOR POWER SPECTRUM RESULTS AT REDSHIFT 7 (2016, result): “For example, Fan et al. (2006) showed that reionization must be complete by z ≈ 6, a result which was confirmed independent of model by McGreer et al. (2015).”
• Lyα and C iii] emission in z = 7–9 Galaxies: accelerated reionization around luminous star-forming systems? (2016, background): “Measurement of the optical depth to electron scattering faced by the CMB reveals that the process is underway by z ' 9 (Planck Collaboration et al. 2015, 2016), while quasar absorption spectra indicate that reionization is largely complete by z ' 6 (e.g., Fan et al. 2006; McGreer et al. 2015).”
• COSMIC REIONIZATION AFTER PLANCK: COULD QUASARS DO IT ALL? (2015, background): “As shown in Figure 2, our reionization history is also consistent with the dark pixel fraction observed in the Lyα and Lyβ forest of z > 6 quasars, which provides a model- independent upper limit of 1 − QHII < 0.11 at z = 5.9 (McGreer et al. 2015).”
• Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionization (2016, background): “Observations of Lyman α opacities in the spectra of quasi-stellar objects (QSOs) at high redshift have shown unambiguously that the Universe becomes nearly transparent to LyC photons (λ ≤ 912Å) at z ∼ 6 (Fan et al. 2001; Becker et al. 2001; Fan et al. 2006; McGreer et al. 2015).”
• Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, background): “The fraction of dark pixels in the Lyα and Lyβ forests provides a model-independent limit on the end of reionization (McGreer 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, methodology): “…derived empirical constraints on the evolution of the ionizing emissivity based on the recently measured Thomson optical depth τ (PC15) and the QH II(z)ʼs inferred from quasar absorption spectra and the prevalence of Lyα emission in z = 7–8 galaxies (Fan et al. 2006b; McGreer et al. 2015; S14).”
• Radiation Backgrounds at Cosmic Dawn: X-Rays from Compact Binaries (2016, background): “2015), the dark pixel statistics (McGreer et al. 2015), and the swift drop observed in the space density of Lyα emitting galaxies at z > 6 (e.g. Choudhury et al. 2015; Schenker et al. 2014).”
• Inferring the astrophysics of reionization and cosmic dawn from galaxy luminosity functions and the 21-cm signal (2018, methodology): “…scattering optical depth to the cosmic microwave background (CMB) (Planck Collaboration et al. 2016b); and (ii) the dark fraction of pixels in QSO spectra (McGreer et al. 2015).16 For (i) we use the latest estimate of the optical depth τe = 0.058±0.012(1σ) from Planck Collaboration et al. (2016b).”
• THE FINAL SDSS HIGH-REDSHIFT QUASAR SAMPLE OF 52 QUASARS AT z > 5.7 (2016, background): “…spectra have revealed strong or even complete absorption in the Lyα forests, indicating that the redshift probed ( ~z 6) is close to the epoch of cosmic reionization (e.g., Becker et al. 2001; White et al. 2003; Fan et al. 2006b; Carilli et al. 2010; Bolton et al. 2011; McGreer et al. 2015).”
• New constraints on lyman-α opacity with a sample of 62 quasars at z > 5.7 (2018, methodology): “A ‘GOLD’ sample is chosen with S/N 11 to match the S/N of the worst spectrum used in McGreer et al. (2015).”
• COSMIC REIONIZATION AND EARLY STAR-FORMING GALAXIES: A JOINT ANALYSIS OF NEW CONSTRAINTS FROM PLANCK AND THE HUBBLE SPACE TELESCOPE (2015, background): “…to z ∼ 7 − 8 from Treu et al. (2013), Pentericci et al. (2014) and Schenker et al. (2014), the Lyman-α damping wing absorption constraints from GRB host galaxies by Chornock et al. (2013), and the number of dark pixels in Lyman-α forest observations of background quasars (McGreer et al. 2015).”
• CONTRASTING GALAXY FORMATION FROM QUANTUM WAVE DARK MATTER, ψDM, WITH ΛCDM, USING PLANCK AND HUBBLE DATA (2015, background): “Recent observations indicate that reionization undergoes a rapid evolution at < <z6 8 and is completed at ~z 6 (Fan et al. 2006; Schroeder et al. 2013; Schenker et al. 2014; McGreer et al. 2015).”
• 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.”