Effective screening due to minihalos during the epoch of reionization

We show that the gaseous halos of collapsed objects introduce a substantial cumulative opacity to ionizing radiation, even after the smoothly distributed hydrogen in the intergalactic medium has been fully reionized. This opacity causes a delay of Deltazgreater than or similar to1 in redshift between the time of the overlap of ionized bubbles in the intergalactic medium and the lifting of complete Gunn-Peterson Lyalpha absorption. The minihalos responsible for this screening effect are not resolved by existing numerical simulations of reionization.