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The brighter galaxies reionized the Universe

Sharma, M, Theuns, T, Frenk, C, Bower, R, Crain, RA, Schaller, M and Schaye, J (2016) The brighter galaxies reionized the Universe. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 458 (1). L94-L98. ISSN 0035-8711

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Hydrogen in the Universe was (re)ionized between redshifts z ≈ 10 and z ≈ 6. The nature of the sources of the ionizing radiation is hotly debated, with faint galaxies below current detection limits regarded as prime candidates. Here, we consider a scenario in which ionizing photons escape through channels punctured in the interstellar medium by outflows powered by starbursts. We take account of the observation that strong outflows occur only when the star formation density is sufficiently high, and estimate the galaxy-averaged escape fraction as a function of redshift and luminosity from the resolved star formation surface densities in the EAGLE cosmological hydrodynamical simulation. We find that the fraction of ionizing photons that escape from galaxies increases rapidly with redshift, reaching values of 5–20 per cent at z > 6, with the brighter galaxies having higher escape fractions. Combining the dependence of escape fraction on luminosity and redshift with the observed luminosity function, we demonstrate that galaxies emit enough ionizing photons to match the existing constraints on reionization while also matching the observed ultraviolet-background post-reionization. Our findings suggest that galaxies above the current Hubble Space Telescope detection limit emit half of the ionizing radiation required to reionize the Universe.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record MNRAS (May 01, 2016) 458 (1): L94-L98. is available online at: http://dx.doi.org/10.1093/mnrasl/slw021
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
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Date Deposited: 19 May 2016 13:10
Last Modified: 02 Aug 2022 15:24
DOI or ID number: 10.1093/mnrasl/slw021
URI: https://researchonline.ljmu.ac.uk/id/eprint/3630
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