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tokens: of ionizing photons drops rapidly, and is therefore quite low when the supernovae start to create clear channels. At these early times, the amount of photons reaching the IGM before the supernova phase is low as well. Similarly, the lower panel of Fig. 9 shows the ionizing duty cycle as a function of halo mass, and , for four regularly log-spaced mass bins centred on log ( M ⋆ /M ⊙ ) = 7.75, 8.25, 8.75 and 9.25. This is in strong disagreement with the recent results of Kimm et al. ( 2017 ), who simulated the formation of mini-haloes and found that f esc can be very high even before the first supernova. However, their study focuses on much lower mass haloes, reaching M vir ≤ 10 8 M ⊙ at most. They also include a description of pop III stars and molecular hydrogen, which can lead to significant differences for haloes below the atomic cooling limit of M vir ∼ 10 8 M ⊙ . Figure 9. Ionizing duty cycle of the two most massive haloes, as a function of the galaxy (upper panel) and halo (lower panel) mass. The blue (red) dashed line shows the fraction of the time a galaxy of a given mass spends with higher than 10 50 (10 48 ) photons per second. On average, a more massive galaxy spends more time leaking LyC photons. On the other side of the mass spectrum, when M ⋆ > 10 6 M ⊙ , the duty cycle saturates, with and . This happens when the galaxy starts to reach a more stable regime, with feedback-regulated star formation, but where the star formation is rarely completely shut off. This means that the gas in the galaxy will usually not have the time to settle down in between two starburst events, leading on average to a more steady production of ionizing photons. 5 LOCAL ESCAPE OF IONIZING RADIATION In Section 4 , we have found that the escape fraction is mainly regulated by the interplay between supernovae, gas accretion and clustered star formation, and we have limited our analysis to the total escape fraction of each galaxy, computed at the virial radius. Because it is strongly linked with ISM-scale phenomena, we will now concentrate on the intrahalo processes leading to the escape of ionizing radiation. For this purpose, we will mainly focus on the most massive galaxy in our sample. 5.1 Does radiation escape from the emission clouds? Before reaching the IGM, the ionizing photons must travel through the complex distribution of gas inside and around the galaxy. Kimm Cen ( 2014 ), Ma et al. ( 2015 ) and Paardekooper et al. ( 2015 ) showed that when f esc is low, most of the photons are absorbed very locally, within 100 pc of their emission point, and that it is indeed crucial to resolve properly the ISM in order to study properly the escape of ionizing radiation. We find very similar results with our simulations, and we suggest that this is the reason behind the strong coupling between the supernova feedback and evolution of f esc . While the idea that clear channels for ionizing radiation from young stars are created by ionizing radiation itself is