Evolution in the escape fraction of ionizing photons and the decline in strong Lyα emission from z > 6 galaxies

Abstract

The rapid decline in the number of strong Lyα emitting galaxiesat z > 6 provides evidence for neutral hydrogen in the intergalactic medium, but is difficult to explain with plausible models for reionization. We demonstrate that the observed reduction in Lyα flux from galaxies at z > 6 can be explained by evolution in the escape fraction of ionizing photons, fesc. We find that the median observed drop in the fraction of galaxies showing strong Lyα emission, as well as the observed evolution of the Lyα luminosity function both follow from a small increase in fesc of Δfesc ∼ 0.1 from fesc ∼ 0.6 at z ∼ 6. This high escape fraction may be at odds with current constraints on the ionizing photon es..