Conditions for Reionizing the Universe with a Low Galaxy Ionizing Photon Escape Fraction

By S. Finkelstein, Anson D’Aloisio, Jan-Pieter Paardekooper, R. Ryan, P. Behroozi, K. Finlator, R. Livermore, P. Sanderbeck, Claudio Dalla Vecchia, S. Khochfar. Astrophysical Journal, 2019

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We explore scenarios for reionizing the intergalactic medium with low galaxy ionizing photon escape fractions. We combine simulation-based halo mass–dependent escape fractions with an extrapolation of the observed galaxy rest-ultraviolet luminosity functions to solve for the reionization history from z = . We explore the posterior distributions for key unknown quantities, including the limiting halo mass for star formation, the ionizing photon production efficiency, and a potential contribution from active galactic nuclei (AGNs). We marginalize over the allowable parameter space using a Markov chain Monte Carlo method, finding a solution that satisfies the most model-independent constraints on reionization. Our fiducial model can match observational constraints with an average escape fraction of <5% throughout the bulk of the epoch of reionization if (i) galaxies form stars down to the atomic cooling limit before reionization and a photosuppression mass of log(Mh/M⊙) ∼ 9 during/after reionization (−13 < MUV,lim < −11), (ii) galaxies become more efficient producers of ionizing photons at higher redshifts and fainter magnitudes, and (iii) there is a significant but subdominant contribution by AGNs at z ≲ 7. In this model, the faintest galaxies (MUV > −15) dominate the ionizing emissivity, leading to an earlier start to reionization and a smoother evolution of the ionized volume-filling fraction than models that assume a single escape fraction at all redshifts and luminosities. The ionizing emissivity from this model is consistent with observations at z = 4–5 (and below, when extrapolated), in contrast to some models that assume a single escape fraction. Our predicted ionized volume-filling fraction at z = 7 of = 78% (±8%) is in modest (∼1σ–2σ) tension with observations of Lyα emitters at z ∼ 7 and the damping-wing analyses of the two known z > 7 quasars, which prefer ∼ 40%–50%.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/fa9eef8265afb9618c74619391c6204c3b135916

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Citations in the corpus

The evolution of the galaxy UV luminosity function at redshifts z ≃ 8 – 15 from deep JWST and ground-based near-infrared imaging (2022, background): “…galaxies could indeed have bathed the Universe in sufficient high-energy photons to produce cosmic hydrogen reionization (Robertson et al. 2015; Finkelstein et al. 2019; Aird et al. 2015), especially since 𝜇- wave background measurements now indicate a ‘mean’ redshift of reionization 〈𝑧〉 '…”
The GLASS-JWST Early Release Science Program. I. Survey Design and Release Plans (2022, background): “…driven by the more numerous, low mass sources with low ionizing photon escape fractions or rarer, high mass sources with enhanced ionizing escape fractions remains a source of debate (e.g., Robertson et al. 2010; Finkelstein et al. 2019; Mason et al. 2019a; Naidu et al. 2020; Matthee et al. 2022).”
Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, methodology): “We illustrate this in the right panel of Figure 10, where we assume Schechter parameters from Finkelstein et al. (2019), ξion from this work, and a constant fesc to evaluate how likely various combinations of fesc and MUV truncation are (as per constraints from Section 2.3).”
CEERS Key Paper. I. An Early Look into the First 500 Myr of Galaxy Formation with JWST (2022, methodology): “We fit the free parameters α and β with an IDL implementation of EMCEE (see Finkelstein et al. 2019 for details).”
The Rise of Faint, Red Active Galactic Nuclei at z > 4: A Sample of Little Red Dots in the JWST Extragalactic Legacy Fields (2025, unknown): “…key to constraining models of BH seeding ( F. Pacucci & A. Loeb 2022; W. Li et al. 2024 ) , the contribution of AGN to hydrogen reionization ( S. L. Finkelstein et al. 2019; E. Giallongo et al. 2019; P. Dayal et al. 2020; L. Y. A. Yung et al. 2021 ) , and the early coevolution of galaxies and BHs…”
Early Results from GLASS-JWST. III. Galaxy Candidates at z ∼9–15 (2022, background): “…in which the Universe was still largely neutral at z∼8 and was rapidly reionized by z ∼ 5.5− 6 (e.g. Mitra et al. 2015; Greig & Mesinger 2017; Mason et al. 2018), likely by faint star-forming galaxies (e.g. Castellano et al. 2016a; Yue et al. 2018; Finkelstein et al. 2019; Dayal et al. 2020).”
The Complete CEERS Early Universe Galaxy Sample: A Surprisingly Slow Evolution of the Space Density of Bright Galaxies at z ∼ 8.5–14.5 (2023, methodology): “We ﬁ t the four free parameters with an IDL implementation of EMCEE ( see Finkelstein et al. 2019 for details ) , taking the median of the posterior as our ﬁ ducial values.”