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Galactic ionizing photon budget during the epoch of reionization in the Cosmic Dawn II simulation


Lewis, Joseph S W; Ocvirk, Pierre; Aubert, Dominique; Sorce, Jenny G; Shapiro, Paul R; Deparis, Nicolas; Dawoodbhoy, Taha; Teyssier, Romain; Yepes, Gustavo; Gottlöber, Stefan; Ahn, Kyungjin; Iliev, Ilian T; Chardin, Jonathan (2020). Galactic ionizing photon budget during the epoch of reionization in the Cosmic Dawn II simulation. Monthly Notices of the Royal Astronomical Society, 496(4):4342-4357.

Abstract

Cosmic Dawn II yields the first statistically meaningful determination of the relative contribution to reionization by galaxies of different halo mass, from a fully coupled radiation-hydrodynamics simulation of the epoch of reionization large enough (∼100 Mpc) to model global reionization while resolving the formation of all galactic haloes above ∼108M⊙⁠. Cell transmission inside haloes is bi-modal – ionized cells are transparent, while neutral cells absorb the photons their stars produce – and the halo escape fraction fesc reflects the balance of star formation rate (SFR) between these modes. The latter is increasingly prevalent at higher halo mass, driving down fesc (we provide analytical fits to our results), whereas halo escape luminosity, proportional to fesc × SFR, increases with mass. Haloes with dark matter masses within 6×108M⊙<Mhalo<3×1010M⊙ produce ∼80 per cent of the escaping photons at z = 7, when the universe is 50 per cent ionized, making them the main drivers of cosmic reionization. Less massive haloes, though more numerous, have low SFRs and contribute less than 10 per cent of the photon budget then, despite their high fesc. High-mass haloes are too few and too opaque, contributing <10 per cent despite their high SFRs. The dominant mass range is lower (higher) at higher (lower) redshift, as mass function and reionization advance together (e.g. at z = 8.5, xH i = 0.9, Mhalo<5×109M⊙ haloes contributed ∼80 per cent). Galaxies with UV magnitudes MAB1600 between −12 and −19 dominated reionization between z = 6 and 8.

Abstract

Cosmic Dawn II yields the first statistically meaningful determination of the relative contribution to reionization by galaxies of different halo mass, from a fully coupled radiation-hydrodynamics simulation of the epoch of reionization large enough (∼100 Mpc) to model global reionization while resolving the formation of all galactic haloes above ∼108M⊙⁠. Cell transmission inside haloes is bi-modal – ionized cells are transparent, while neutral cells absorb the photons their stars produce – and the halo escape fraction fesc reflects the balance of star formation rate (SFR) between these modes. The latter is increasingly prevalent at higher halo mass, driving down fesc (we provide analytical fits to our results), whereas halo escape luminosity, proportional to fesc × SFR, increases with mass. Haloes with dark matter masses within 6×108M⊙<Mhalo<3×1010M⊙ produce ∼80 per cent of the escaping photons at z = 7, when the universe is 50 per cent ionized, making them the main drivers of cosmic reionization. Less massive haloes, though more numerous, have low SFRs and contribute less than 10 per cent of the photon budget then, despite their high fesc. High-mass haloes are too few and too opaque, contributing <10 per cent despite their high SFRs. The dominant mass range is lower (higher) at higher (lower) redshift, as mass function and reionization advance together (e.g. at z = 8.5, xH i = 0.9, Mhalo<5×109M⊙ haloes contributed ∼80 per cent). Galaxies with UV magnitudes MAB1600 between −12 and −19 dominated reionization between z = 6 and 8.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute for Computational Science
Dewey Decimal Classification:530 Physics
Scopus Subject Areas:Physical Sciences > Astronomy and Astrophysics
Physical Sciences > Space and Planetary Science
Uncontrolled Keywords:Space and Planetary Science, Astronomy and Astrophysics
Language:English
Date:21 August 2020
Deposited On:15 Feb 2021 09:52
Last Modified:16 Feb 2021 21:00
Publisher:Oxford University Press
ISSN:0035-8711
OA Status:Green
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1093/mnras/staa1748

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