The Proximity Effect Around High Redshift Galaxies

Recent observations have shown that the intergalactic medium (IGM) is more transparent to Lyα photons close to Lyman Break Galaxies (LBGs) than at large distance from them, i.e. a proximity effect. Cosmological simulations including winds from LBGs have been so far unable to explain this trend. By coupling such simulations with the radiative transfer code CRASH, we investigate whether the addition of the ionizing radiation emitted by LBGs can increase the transmissivity by decreasing the neutral hydrogen fraction in the inner Mpc of the galaxy halo. The transmissivity as a function of distance is roughly reproduced only if LBGs are identified with dwarf galaxies (with masses < ∼ 109M⊙) which are undergoing a vigorous (50M⊙ yr ) burst of star formation. Similar star formation rates in larger galaxies are not sufficient to overwhelm the large recombination rates associated with their denser environment. If so, photoionization partly reconciles theory with data, although we discuss the considerable uncertainties still present in both approaches.