Undetected sources aleow transmission of the Lyα line from gaeaxies prior to reionization

Abstract

The discovery of Lyα emission from galaxies at redshifts beyond z ∼ 6.5 should not be naively interpreted as implying that the intergalactic medium (IGM) had been reionized at higher redshifts. We show that a cluster of faint undetected sources around each observed galaxy can increase the volume of the galaxy's H II region by an order of magnitude. As a result, we find that the H II regions around massive galaxies would have been large enough to allow transmission of the galaxy's Lyα line prior to reionization. We also show that quasars may contribute a significant fraction of the ionizing photons to H II regions around galaxies with a velocity dispersion larger than ∼ 100 km s-1. These contributing quasars are not usually seen because of the small fraction of time they spend in a luminous phase.