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

Finkelstein, Steven L.; D’Aloisio, Anson; Paardekooper, Jan-Pieter; Ryan, Russell, Jr.; Behroozi, Peter; Finlator, Kristian; Livermore, Rachael; Upton Sanderbeck, Phoebe R.; Dalla Vecchia, Claudio; Khochfar, Sadegh
Referencia bibliográfica

The Astrophysical Journal, Volume 879, Issue 1, article id. 36, 34 pp. (2019).

Fecha de publicación:
7
2019
Número de autores
10
Número de autores del IAC
1
Número de citas
280
Número de citas referidas
238
Descripción
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 = 20\to 4. 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(M h/M ⊙) ∼ 9 during/after reionization (‑13 < M UV,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 (M UV >‑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 {Q}{{{H}}II}} = 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 {Q}{{{H}}II},z=7} ∼ 40%–50%.
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Astrofísica Numérica: Formación y Evolución de Galaxias
Entre las cuestiones fundamentales en Astronomía y Astrofísica están la formación y evolución de galaxias. Las escalas de tiempo y tamaño son tan astronómicas que su observación en galaxias individuales es imposible. Solo con el uso de simulaciones numéricas es posible entender la formación de estructuras cósmicas dentro del actual marco
Claudio
Dalla Vecchia