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

Autor: Finkelstein, Steven L., D'Aloisio, Anson, Paardekooper, Jan-Pieter, Ryan Jr., Russell, Behroozi, Peter, Finlator, Kristian, Livermore, Rachael, Sanderbeck, Phoebe R. Upton, Vecchia, Claudio Dalla, Khochfar, Sadegh
Rok vydání: 2019
Předmět:
Druh dokumentu: Working Paper
DOI: 10.3847/1538-4357/ab1ea8
Popis: 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 z=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 (AGN). We marginalize over the allowable parameter space using a Markov Chain Monte Carlo method, finding a solution which 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/Msol)~9 during/after reionization (-13-15) dominate the ionizing emissivity, leading to an earlier start to reionization and a smoother evolution of the ionized volume filling fraction than models which 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 which assume a single escape fraction. Our predicted ionized volume filling fraction at z=7 of Q_HII=78% (+\- 8%) is in ~1-2 sigma tension with observations of Lya emitters at z~7 and the damping wing analyses of the two known z>7 quasars, which prefer Q_HII,z=7~40-50%.
Comment: 45 pages, 21 figures, accepted for publication in the Astrophysical Journal
Databáze: arXiv
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