Escape of ionizing radiation from star-forming regions in young galaxies

Using results from high-resolution galaxy formation simulations in a standard Lambda CDM cosmology and a fully conservative multiresolution radiative transfer code around point sources, we compute the energy-dependent escape fraction f(esc) of ionizing photons from a large number of star-forming regions in two galaxies at five different redshifts from to 2.39. All escape fractions show a monotonic decline with time, from (at the Lyman z p 3.8 limit) similar to 6%-10% at to 1%-2% at z = 2.39 due to higher gas clumping at lower redshifts. It appears that inceased feedback can lead to higher f(esc) at z greater than or similar to 3.4 via the evacuation of gas from the vicinity of star-forming regions and to lower f(esc) at z less than or similar to 2.39 through the accumulation of swept-up shells in denser environment. Our results agree well with the observational findings of Inoue et al. on the redshift evolution of f(esc) in the redshift interval z = 2-3.6.