COSMIC REIONIZATION AFTER PLANCK: COULD QUASARS DO IT ALL?

By P. Madau, F. Haardt. 2015

267 citations recorded by the source corpus.

We assess a model of late cosmic reionization in which the ionizing background radiation arises entirely from high-redshift quasars and other active galactic nuclei (AGNs). The low optical depth to Thomson scattering reported by the Planck Collaboration pushes the redshift of instantaneous reionization down to z = 8.8 − 1.4 + 1.7 ?> and greatly reduces the need for significant Lyman-continuum emission at very early times. We show that if recent claims of a numerous population of faint AGNs at z = 4–6 are upheld and the high inferred AGN comoving emissivity at these epochs persists to higher, z ≳ 10, redshifts, then active galaxies may drive the reionization of hydrogen and helium with little contribution from normal star-forming galaxies. We discuss an AGN-dominated scenario that satisfies a number of observational constraints: the H i photoionization rate is relatively flat over the range 2 < z < 5, hydrogen gets fully reionized by z ≃ 5.7, and the integrated Thomson scattering optical depth is τ ≃ 0.056, in agreement with measurements based on the Lyα opacity of the intergalactic medium (IGM) and cosmic microwave background polarization. It is a prediction of the model that helium gets doubly reionized before redshift 4, the heat input from helium reionization dominates the thermal balance of the IGM after hydrogen reionization, and z > 5 AGNs provide a significant fraction of the unresolved X-ray background at 2 keV. Singly and doubly ionized helium contribute about 13% to τ, and the He iii volume fraction is already 50% when hydrogen becomes fully reionized.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/31f22b56eabb8229d9af6895a035794d555bec6b

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In Astronomy and Astrophysics

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

In Instrumentation

1. Richard S. Ellis
2. R. Bouwens
3. P. Oesch
4. G. Illingworth
5. M. Trenti
6. M. McQuinn
7. P. Madau
8. M. Franx

Citations in the corpus

• Evolution of the AGN UV luminosity function from redshift 7.5 (2018, methodology): “The large quasar emissivity adopted by Madau & Haardt (2015) results in an early completion of He ii reionization at z ≈ 4, which is inconsistent with the measured strong He ii absorption at 2.7 < z < 3 (Worseck et al. 2016; Mitra et al. 2018; Puchwein et al. 2018) if the He ii-ionizing background…”
• SUBARU HIGH-z EXPLORATION OF LOW-LUMINOSITY QUASARS (SHELLQs). I. DISCOVERY OF 15 QUASARS AND BRIGHT GALAXIES AT 5.7 < z < 6.9 (2016, unknown): “…as a possible additional source of ionizing photons (e.g., Lehnert & Bremer 2003; Fontanot et al. 2012; Grissom et al. 2014; Giallongo et al. 2015; Madau & Haardt 2015), but the results are still controversial, largely due to the lack of knowledge about the numbers of faint quasars and AGNs…”
• THE FINAL SDSS HIGH-REDSHIFT QUASAR SAMPLE OF 52 QUASARS AT z > 5.7 (2016, background): “Figure 11 shows that we cannot yet fully rule out the possibility that UV light from AGNs is responsible for ionizing the universe (see also e.g., Giallongo et al. 2015; Madau & Haardt 2015; Mitra et al. 2016).”
• The Evolution of the Intergalactic Medium (2015, methodology): “An issue with this model is that, if quasars reionized the hydrogen, their hard spectrum would also doubly ionize the helium by z = 4 (Madau & Haardt 2015), in conflict with the He ii Gunn Peterson trough detections and the IGM temperature measurements (§ 2.5 and § 2.3, respectively).”
• The Universe Is Reionizing at z ∼ 7: Bayesian Inference of the IGM Neutral Fraction Using Lyα Emission from Galaxies (2017, background): “…2012a; Robertson et al. 2013; Schmidt cmason@astro.ucla.edu et al. 2014), though a contribution from AGN cannot be excluded (Giallongo et al. 2015; Madau & Haardt 2015; Onoue et al. 2017): we do not know if sufficient hard ionizing photons escape from galaxies as we do not fully understand the…”
• Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies (2016, unknown): “E-mail: izotov@mao.kiev.ua an important role (Madau & Haardt 2015).”
• Radiation Backgrounds at Cosmic Dawn: X-Rays from Compact Binaries (2016, background): “We have solved the above ODE for a galaxy-dominated scenario (cf. Madau & Haardt 2015), assuming the ionized gas is at temperature TK = 10 4.3K and has clumping factor CRR = 2.9[(1 + z)/6] −1.1 (Shull et al. 2012) (both TK and CRR determine the case-B radiative recombination rate).”
• J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons (2017, background): “While Madau & Haardt (2015) considered active galactic nuclei (AGN) as possible alternative sources of the ionization, more recent studies (Hassan et al. 2018; Mitra, Choudhury & Ferrara 2013) show that the contribution of AGNs to the reionization of the Universe was small.”
• Low-redshift Lyman continuum leaking galaxies with high [O iii]/[O ii] ratios (2018, background): “While there are pro and con arguments on the role of AGN in the reionization of the Universe (e.g. Madau & Haardt 2015; Hassan et al. 2018; Mitra, Choudhury & Ferrara 2018; Parsa, Dunlop & McLure 2018), their contribution remains uncertain.”
• Lyman-α spectral properties of five newly discovered Lyman continuum emitters (2016, background): “A new population of faint Active Galactive Nuclei (AGNs) has been recently reported (Giallongo et al. 2015), which could sustain reionisation, assuming that their escape fraction of ionising photons is high (e.g. 100% in Madau & Haardt 2015).”
• Consistent modelling of the meta-galactic UV background and the thermal/ionization history of the intergalactic medium (2018, methodology): “The galaxy plus AGN picture has been recently questioned by Madau & Haardt (2015) (hereinafter MH15), who showed how a significant population of previously undetected faint AGN at 4 ∼< z ∼< 6.5, claimed by Giallongo et al. (2015), may actually dominate H I reionization (albeit with a somewhat…”
• The z ∼ 6 Luminosity Function Fainter than −15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties (2016, background): “While much evidence suggests that the process might be driven by galaxies (e.g., Robertson et al. 2013, 2015; Mitra et al. 2015; Bouwens et al. 2015b), others have suggested that quasars could provide the dominant contribution (Giallongo et al. 2015; Madau & Haardt 2015; Mitra et al. 2016).”