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A Census of the LyC Photons that Form the UV Background During Reionization

Published version
Peer-reviewed

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Authors

Katz, Harley 
Kimm, Taysun 
Rosdahl, Joakim 

Abstract

We present a new, on-the-fly photon flux and absorption tracer algorithm designed to directly measure the contribution of different source populations to the metagalactic UV background and to the ionisation fraction of gas in the Universe. We use a suite of multifrequency radiation hydrodynamics simulations that are carefully calibrated to reproduce a realistic reionization history and galaxy properties at z≥6, to disentangle the contribution of photons emitted by different mass haloes and by stars with different metallicities and ages to the UV background during reionization. While at very early cosmic times low mass, metal poor haloes provide most of the LyC photons, their contribution decreases steadily with time. At z=6 it is the photons emitted by massive systems (Mhalo/M>1010h−1) and by the metal enriched stars (10−3<Z/Z<10−1.5) that provide the largest contribution to the ionising UV background. We demonstrate that there are large variations in the escape fraction depending on the source, with the escape fraction being highest (∼45−60%) for photons emitted by the oldest stars that penetrate into the IGM via low opacity channels carved by the ionising photons and supernova from younger stars. Before HII regions begin to overlap, the photoionisation rate strongly fluctuates between different, isolated HII bubbles, depending on the embedded ionising source, which we suggest may result in spatial variations in the properties of dwarf galaxies.

Description

Keywords

astro-ph.CO, astro-ph.CO, astro-ph.GA, radiative transfer, dark ages, reionization, first stars

Journal Title

Monthly Notices of the Royal Astronomical Society

Conference Name

Journal ISSN

0035-8711
1365-2966

Volume Title

478

Publisher

Oxford University Press
Sponsorship
European Research Council (320596)
Science and Technology Facilities Council (ST/N000927/1)
Science and Technology Facilities Council (ST/L000725/1)
European Research Council (638707)
Science and Technology Facilities Council (ST/P002315/1)
Science and Technology Facilities Council (ST/S002626/1)
Science and Technology Facilities Council (ST/R002452/1)
Science and Technology Facilities Council (ST/R00689X/1)