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arXiv · 1902.02792

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

Steven L. Finkelstein·Anson D'Aloisio·Jan-Pieter Paardekooper·Russell Ryan Jr.·Peter Behroozi·Kristian Finlator·Rachael Livermore·Phoebe R. Upton Sanderbeck·Claudio Dalla Vecchia·Sadegh Khochfar
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Abstract

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%.

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BibTeXRIS

Steven L. Finkelstein, Anson D'Aloisio, Jan-Pieter Paardekooper, Russell Ryan Jr., Peter Behroozi, Kristian Finlator, Rachael Livermore, Phoebe R. Upton Sanderbeck, Claudio Dalla Vecchia, Sadegh Khochfar. 2019-05-02. Conditions for Reionizing the Universe with A Low Galaxy Ionizing Photon Escape Fraction. https://doi.org/10.3847/1538-4357%2Fab1ea8

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