The SPHINX cosmological simulations of the first billion years: The impact of binary stars on reionization

Joakim Rosdahl, Harley Katz, Jérémy Blaizot, Taysun Kimm, Léo Michel-Dansac, Thibault Garel, Martin Haehnelt, Pierre Ocvirk, Romain Teyssier

Research output: Contribution to journalArticlepeer-review

135 Citations (Scopus)


We present the SPHINX suite of cosmological adaptive mesh refinement simulations, the first radiation-hydrodynamical simulations to simultaneously capture large-scale reionization and the escape of ionizing radiation from thousands of resolved galaxies. Our 5 and 10 co-moving Mpc volumes resolve haloes down to the atomic cooling limit and model the interstellar medium with better than ≈ 10 pc resolution. The project has numerous goals in improving our understanding of reionization and making predictions for future observations. In this first paper, we study how the inclusion of binary stars in computing stellar luminosities impacts reionization, compared to a model that includes only single stars. Owing to the suppression of galaxy growth via strong feedback, our galaxies are in good agreement with observational estimates of the galaxy luminosity function. We find that binaries have a significant impact on the timing of reionization: with binaries, our boxes are 99.9 percent ionized by volume at z ≈ 7, while without them our volumes fail to reionize by z = 6. These results are robust to changes in volume size, resolution, and feedback efficiency. The escape of ionizing radiation from individual galaxies varies strongly and frequently. On average, binaries lead to escape fractions of ≈ 7-10 percent, about three times higher than with single stars only. The higher escape fraction is a result of a shallower decline in ionizing luminosity with age, and is the primary reason for earlier reionization, although the higher integrated luminosity with binaries also plays a subdominant role.

Original languageEnglish
Pages (from-to)994-1016
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - 2018 Sep 1

Bibliographical note

Funding Information:
We are grateful to the reviewer, John Wise, for comments that strengthened the ppaper. We thank Dominique Aubeprt, Leindert Boogaard, Julien Devriendt, Yohan Dubois, Peter Mitchell, Ali Rahmati, Benoit Semelin, and Maxime Trebitsch for useful discussions, and Andreas Bleuler for very useful contributions to the optimization of RAMSES-RT. JR and JB acknowledge support from the ORAGE project from the Agence Nationale de la Recherche under grant ANR-14-CE33-0016-03. HK thanks the Beecroft fellowship, the Nicholas Kurti Junior Fellowship, and Brasenose College. TK is supported 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). TG is grateful to the LABEX Lyon Institute of Origins (ANR-10-LABX-0066) of the Université de Lyon for its financial support within the programme ‘Investisse-ments d’Avenir’ (ANR-11-IDEX-0007) of the French government operated by the National Research Agency (ANR). Support by ERC Advanced Grant 320596 ‘The Emergence of Structure during the Epoch of reionization’ is gratefully acknowledged. The results of this research have been achieved using the PRACE Research Infrastructure resource SuperMUC based in Garching, Germany. We are grateful for the excellent technical support provided by the SuperMUC staff. Preparations and tests were also performed at the Common Computing Facility (CCF) of the LABEX Lyon Institute of Origins (ANR-10-LABX-0066), and on the GENCI national computing centres at CCRT and CINES (DARI grant number x2016047376). Available at

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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