tokens: and thus star formation (see Gnedin 2000 ; Wise Abel 2008a ). Lastly, because ionizing radiation originates from massive stars, the fraction of halos generating escaping photons, shown in the right panel of Figure 22 , follow a similar trend as the stellar occupation fraction. Figure 22. Fractions of halos with active star formation (left; stars younger than 20 Myr) and photons escaped from their virial radius (right) as a function of the halo mass for the Rarepeak region (dashed blue) at z = 15, Normal region (solid black) at z = 15, 12.5, and Void region (red solid with boxes) at z = 15, 10, 8. 4.5. Comparison to Other Work Early efforts to constrain the escape fraction with simulations found wildly varying f esc values over a range of halo masses 10 7 –10 12 , ranging from less than 1% to unity (e.g., Fujita et al. 2003 ; Razoumov Sommer-Larsen 2006 ; Gnedin et al. 2008 ; Wise Cen 2009 ; Paardekooper et al. 2011 ; Yajima et al. 2011 ). However, in the past few years with higher resolution simulations that resolve star-forming clouds, there has been some convergence, showing that low-mass () halos have higher mean f esc values ≳25% (Wise et al. 2014 ; Paardekooper et al. 2015 ) that then decrease with halo mass to approach ∼5%–15% in more massive (log M vir / = 8–11) galaxies at z ≥ 6 (Kimm Cen 2014 ; Ma et al. 2015 ). Using the star formation surface density as a proxy to f esc , Sharma et al. ( 2016 ) suggested that the brightest galaxies dominated the photon budget at the end of reionization with 50% of the photons originating from galaxies with UV absolute magnitudes M 1500 ≤ (−18, −16.5) and at z = (6, 8), respectively. Our results are in agreement with these latest works with f esc decreasing with halo mass, given that M vir ≲ 10 9 . Here we only compare the mean values, but in reality, it should be noted that escape fractions greatly vary between galaxies and temporally. In the smallest galaxies, mean f esc values are ∼50% in the range of 10 7 –10 7.5 with a large scatter (see Wise et al. 2014 ; Paardekooper et al. 2015 ), spanning the full range from zero to unity, depending on previously discussed conditions. This then decreases to ∼0.05 at higher halo masses, agreeing with Kimm Cen ( 2014 ) and Ma et al. ( 2015 ). The Void simulation at z = 8 contains two galaxies with M ⋆ ≃ 3 × 10 7 contained in halos with M vir = 2 × 10 9 that have escape fractions of 25% that are undergoing strong starbursts. These galaxies may be analogs of the ones explored in the “brightest galaxies reionized the universe” scenario posed by Sharma et al. ( 2016 ). In the same data, we are also in agreement with Sharma et al., where we both find that 50% of the ionizing photons (see Figure 18 ) come from galaxies with an SFR ≥ 0.1 yr −1 in halos M vir ≥ 10 9 at z = 8. 5. CONCLUSIONS In this paper, we have quantified the properties and the UV escape fraction of galaxies during the epoch of reionization, expanding upon the work of Wise et al. ( 2014 ) with
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