Relative escape fraction f_esc, rel ≡ f_esc, LyC/f_esc, UV as a function of ξ_ion, 0 is plotted in green, assuming star-forming galaxies solely drove reionization. Since the dust attenuation estimated for (non-ionizing) UV wavelengths is negligible (f_esc, UV = 1), f_esc, rel equals f_esc, LyC. We also approximated that, for small f_esc, LyC, ξ_ion ≈ ξ_ion, 0. The green region was derived in the analysis of Bouwens et al. (2015) by making use of important constraints on reionization (see Table 1 of Bouwens et al. 2015 for a complete list). The blue region shows the range of ξ_ion, 0 inferred in the present study for faint galaxies, i.e. ξ_ion, 0 = 25.36 ± 0.08. The corresponding constraints we can place on f_esc, rel of ≈8–20% are indicated by the dashed lines. See Sect. 5.3.