  Recent observations have shown that the intergalactic medium (IGM) is more
transparent to Lyalpha photons close to Lyman Break Galaxies (LBGs) than at
large distance from them, ie 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
< 10^9 solar masses), which are undergoing a vigorous (50 solar masses/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
observations, although we discuss a number of uncertainties affecting both
approaches.
