Conditions for reionizing the universe with a low galaxy ionizing photon escape fraction
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 fro...
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| Main Authors: | , , , , , , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
2 May 2019
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| In: |
The astrophysical journal
Year: 2019, Volume: 879, Issue: 1 |
| ISSN: | 1538-4357 |
| DOI: | 10.3847/1538-4357/ab1ea8 |
| Online Access: | Verlag, Volltext: http://dx.doi.org/10.3847/1538-4357/ab1ea8 Verlag, Volltext: http://arxiv.org/abs/1902.02792 
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| Author Notes: | 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, and Sadegh Khochfar |
| Summary: | 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<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 sub-dominant, contribution by AGN 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 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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| Item Description: | Gesehen am 29.08.2019 |
| Physical Description: | Online Resource |
| ISSN: | 1538-4357 |
| DOI: | 10.3847/1538-4357/ab1ea8 |