Galactic ionising photon budget during the Epoch of Reionisation in the Cosmic Dawn II simulation [article]

Joseph S. W. Lewis, Pierre Ocvirk, Dominique Aubert, Jenny G. Sorce, Paul R. Shapiro, Nicolas Deparis, Taha Dawoodbhoy, Romain Teyssier, Gustavo Yepes, Stefan Gottlöber, Kyungjin Ahn, Ilian T. Iliev (+1 others)
2020 arXiv   pre-print
Cosmic Dawn ("CoDa") 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 halos above ∼ 10^8 M_. Cell transmission inside high-mass haloes is bi-modal – ionized cells are transparent, while neutral cells absorb the photons
more » ... stars produce - and the halo escape fraction f_esc reflects the balance of star formation rate ("SFR") between these modes. The latter is increasingly prevalent at higher halo mass, driving down f_esc (we provide analytical fits to our results), whereas halo escape luminosity, proportional to f_esc×SFR, increases with mass. Haloes with dark matter masses within 6.10^8 M_ < M_h < 3.10^10 M_ produce ∼ 80 photons at z=7, when the Universe is 50 of cosmic reionization. Less massive haloes, though more numerous, have low SFRs and contribute less than 10 f_esc. High mass haloes are too few and too opaque, contributing <10 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, x_ HI=0.9, M_h < 5.10^9 M_ haloes contributed ∼80 dominated reionization between z=6 and 8.
arXiv:2001.07785v3 fatcat:je4c3gp7jrdrfjn4agwlpfpmtq