Photoevaporation of cosmological minihaloes during reionization

Energy released by a small fraction of the baryons in the universe, which condensed out while the IGM was cold, dark, and neutral, reheated and reionized it by redshift 6, exposing other baryons already condensed into dwarf-galaxy minihalos to the glare of ionizing radiation. We present the first gas dynamical simulations of the photoevaporation of cosmological minihalos overtaken by the ionization fronts which swept through the IGM during the reionization epoch in the currently-favored ΛCDM universe, including the effects of radiative transfer. These simulations demonstrate the phenomenon of I-front trapping inside minihalos, in which the weak, R-type fronts which traveled supersonically across the IGM decelerated when they encountered the dense, neutral gas inside minihalos, and were thereby transformed into D-type I-fronts, preceded by shock waves. For a minihalo with virial temperature below 10 4 K, the I-front gradually burned its way through the minihalo which trapped it, removing all of its baryonic gas by causing a supersonic, evaporative wind to blow backwards into the IGM, away from the exposed layers of minihalo gas just behind the advancing I-front.