The fraction of ionizing photons escaping from galaxies, $f_{ esc}$, is at the same time a crucial parameter in modelling reionization and a very poorly known quantity, especially at high redshift. Recent observations are starting to constrain the values of $f_{ esc}$ in low-z star-forming galaxies, but the validity of this comparison remains to be verified. Applying at high-z the empirical relation between $f_{ esc}$ and the UV slope trends derived from the Low-z Lyman Continuum Survey, we use the DELPHI semi-analytical galaxy formation model to estimate the global ionizing emissivity of high-z galaxies, which we use to compute the resulting reionization history. We find that both the global ionizing emissivity and reionization history match the observational constraints. Assuming that the low-z correlations hold during the epoch of reionization, we find that galaxies with $-16 \lesssim M_{ UV} \lesssim -13.5$ are the main drivers of reionization. We derive a population-averaged $\langle f_{ esc} \rangle \simeq 8\%, 10\%, 20\%$ at z=4.5, 6, 8.
Categories: astro-ph.GA astro-ph.CO