Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionisation

Reionization in the early Universe is likely driven by dwarf galaxies. Using cosmological radiation-hydrodynamic simulations, we study star formation and the escape of Lyman continuum (LyC) photons from mini-haloes with Mhalo ≲ 10^8 M⊙. Our simulations include a new thermo-turbulent star formation model, non-equilibrium chemistry and relevant stellar feedback processes (photoionization by young massive stars, radiation pressure and mechanical supernova explosions). We find that feedback reduces star formation very efficiently in minihaloes, resulting in the stellar mass consistent with the slope and normalization reported in Kimm&Cen; and the empirical stellarmass-to-halomass relation derived in the local Universe. Because star formation is stochastic and dominated by a few gas clumps, the escape fraction in mini-haloes is generally determined by radiation feedback (heating due to photoionization), rather than supernova explosions.We also find that the photon number-weighted mean escape fraction in mini-haloes is higher (∼20–40 per cent) than that in atomic-cooling haloes, although the instantaneous fraction in individual haloes varies significantly. The escape fraction from Pop III stars is found to be significant (≳10 per cent) only when the mass is greater than ∼100 M⊙. Based on simple analytic calculations, we showthat LyC photons from mini-haloes are, despite their high escape fractions, of minor importance for reionization due to inefficient star formation. We confirm previous claims that stars in atomic-cooling haloes with masses 10^8 M⊙ ≲ Mhalo ≲ 10^11 M⊙ are likely to be the most important source of reionization.