The escape fraction of ionizing photons from high-redshift galaxies from data-constrained reionization models

The escape fraction, f(esc), of ionizing photons from high-redshift galaxies is a key parameter to understand cosmic reionization and star formation history. Yet, in spite of many efforts, it remains largely uncertain. We propose a novel, semi-empirical approach based on a simultaneous match of the most recently determined luminosity functions of galaxies in the redshift range 6 <= z <= 10 with reionization models constrained by a large variety of experimental data. From this procedure, we obtain the evolution of the best-fitting values of f(esc) along with their 2 sigma limits. We find that, averaged over the galaxy population, (i) the escape fraction increases from f(esc) = 0.068(-0.047)(+0.054) at z = 6 to f(esc) = 0.179(-0.132)(+0.331) at z = 8 and (ii) at z = 10 we can only put a lower limit of f(esc) > 0.146. Thus, although errors are large, there is an indication of a 2.6 times increase of the average escape fraction from z = 6 to 8, which might partially release the 'starving reionization' problem.