A Census of the LyC photons that form the UV background during reionization

Harley Katz, Taysun Kimm, Martin Haehnelt, Debora Sijacki, Joakim Rosdahl, Jeremy Blaizot

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)

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 ultraviolet (UV) background and to the ionization 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 starswith 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 Lyman continuum photons, their contribution decreases steadily with time. At z = 6 it is the photons emitted by massive systems (Mhalo/M > 1010 h-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 per cent) for photons emitted by the oldest stars that penetrate into the intergalactic medium via low opacity channels carved by the ionising photons and supernova from younger stars. Before HII regions begin to overlap, the photoionization 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.

Original languageEnglish
Pages (from-to)4986-5005
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Volume478
Issue number4
DOIs
Publication statusPublished - 2018 Aug 21

Bibliographical note

Funding Information:
This work was performed using the DiRAC/Darwin Supercomputer hosted by the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/), provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and funding from the Science and Technology Facilities Council.

Funding Information:
This work used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility (www.dirac.ac.uk). This equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC DiRAC Operations grant ST/K0003259/1. DiRAC is part of the National E-Infrastructure Furthermore, this work used the DiRAC Data Centric system at Durham University, operated by the Institute for Computational Cosmology on behalf of the STFR DiRAC HPC Facility (www.dirac.ac.uk). This equipment was funded by the BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grant ST/K00087X/1, DiRAC operations grant ST/K003267/1 and Durham University. Dirac is part of the National E-Infrastructure.

Funding Information:
PYNBODYHK thanks Girish Kulkarni for useful discussions and comments on this manuscript. This work made considerable use of the open source analysis software (Pontzen et al. 2013). HK thanks Foundation Boustany, the Cambridge Overseas Trust, and the Isaac Newton Studentship. HK also thanks Brasenose College and the support of the Nicholas Kurti Junior Fellowship as well as the Beecroft Fellowship. Support by ERC Advanced Grant 320596 ‘The Emergence of Structure during the Epoch of reionization’ is gratefully acknowledged. DS acknowledges support by STFC and ERC Starting Grant 638707 ‘Black holes and their host galaxies: coevolution across cosmic time’. TK acknowledges support by the National Research Foundation of Korea to the Center for Galaxy Evolution Research (No. 2017R1A5A1070354) and in part by the Yonsei University Future-leading Research Initiative of 2017 (RMS2-2017-22-0150). JR and JB acknowledge support from the ORAGE project from the Agence Nationale de la Recherche under grand ANR-14-CE33-0016-03.

Funding Information:
PYNBODYHK thanks Girish Kulkarni for useful discussions and comments on this manuscript. This work made considerable use of the open source analysis software (Pontzen et al. 2013). HK thanks Foundation Boustany, the Cambridge Overseas Trust, and the Isaac Newton Studentship. HK also thanks Brasenose College and the support of the Nicholas Kurti Junior Fellowship as well as the Beecroft Fellowship. Support by ERC Advanced Grant 320596 'The Emergence of Structure during the Epoch of reionization' is gratefully acknowledged. DS acknowledges support by STFC and ERC Starting Grant 638707 'Black holes and their host galaxies: coevolution across cosmic time'. TK acknowledges support by the National Research Foundation of Korea to the Center for Galaxy Evolution Research (No. 2017R1A5A1070354) and in part by the Yonsei University Future-leading Research Initiative of 2017 (RMS2-2017-22-0150). JR and JB acknowledge support from the ORAGE project from the Agence Nationale de la Recherche under grand ANR-14-CE33-0016-03. This work was performed using the DiRAC/Darwin Supercomputer hosted by the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/), provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and funding from the Science and Technology Facilities Council. This work used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility (www.dirac.ac.uk). This equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC DiRAC Operations grant ST/K0003259/1. DiRAC is part of the National E-Infrastructure Furthermore, this work used the DiRAC Data Centric system at Durham University, operated by the Institute for Computational Cosmology on behalf of the STFR DiRAC HPC Facility (www.dirac.ac.uk). This equipment was funded by the BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grant ST/K00087X/1, DiRAC operations grant ST/K003267/1 and Durham University. Dirac is part of the National E-Infrastructure.

Publisher Copyright:
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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