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tokens: massive star clusters (or OB associations) is a power-law with slope ξ ≃ −2 ± 0.5 (Rosolowsky 2005 ; Hopkins 2012 ): where, assuming ξ = −2 (Hopkins 2012 ), we find A = M *, gal /Λ, with . Assuming M ⊙ and M ⊙ , we estimate Λ ≈ 9.2. Therefore, assuming an escape fraction from the atomic phase of the ISM in the galaxy (defined excluding the absorption due to the molecular cloud) that is constant as a function of the cluster mass, we find: Therefore, as anticipated before in Section 3.3 , in the local Universe (fiducial clouds) the escaping ionizing radiation from a galaxy is produced by roughly equal contribution from small and large mass star clusters, and the number of escaping photons is ∼10 59 per unit solar mass in stars. Therefore, the total escaping radiation is quite insensitive to the upper and lower mass limits of the mass distribution of OB associations. Compact star clusters are similar but with ∼10 times more ionizing photons per mass in stars. For very compact clouds (100 times denser than the fiducial clouds) the escaping ionizing radiation is dominated by the few most massive star clusters in the galaxy, and the number of escaping photons per units star mass is about 40 times higher than for the fiducial clouds. Also, if we make the simple assumption that the mass of the most massive star cluster is related to the total stellar mass M *, gal of the galaxy, by setting , we find . Hence, if star clusters in high-redshift galaxies form in very compact molecular clouds, massive galaxies would be more efficient contributor to propel reionization than dwarf galaxies. Of course the discussion above is only valid if is constant not only as a function of the star cluster mass but also as a function of the mass of the galaxy. Similar to S esc, tot , we can estimate the total emitted ionizing radiation by OB association: and the mean escape fraction from a galaxy by taking the ratio : This last equation confirms that from galaxies in the local Universe (fiducial clouds) is extremely small , and only assuming that molecular clouds at redshift z > 6 were 100× denser than in the local Universe is possible to propel reionization with UV radiation from massive stars in galaxies. 5 SUMMARY AND CONCLUSIONS In this paper, the second of a series, we calculate the hydrogen- and helium-ionizing radiation escaping realistic young star cluster forming in turbulent molecular clouds. To the best of our knowledge this is the first work in which is calculated by self-consistently simulating the formation, UV radiation feedback, and contribution to the escaping ionizing radiation from individual massive stars producing the observed IMF slope and normalization. We used a set of high-resolution radiation-magnetohydrodynamic simulations of star formation in self-gravitating, turbulent molecular clouds presented in He et al. ( 2019 ), in which we vary the mass of the star-forming molecular clouds between m gas = 10 3 M ⊙ and 3 × 10 5 M ⊙ and adopt gas