The escape of ionising radiation from galaxies during the epoch of reionisation

The appearance of the first luminous sources in the Universe marks the beginning of the epoch of reionisation. The cosmic reionisation of hydrogen has been the last major phase transition in the evolution of the Universe, turning cool neutral gas into the hot, ionised plasma we observe today. Up to now, direct observations of reionisation have been impossible, most of our current knowledge therefore stems from numerical studies. This is expected to change soon, though. Galaxy surveys at high redshifts are beginning to probe this important epoch and upcoming 21-cm experiments will provide hints on the distribution of neutral hydrogen during reionisation. For this reason a lot of theoretical effort has gone into understanding the cosmic reionisation process. However, even with current computing facilities the modelling of the reionisation epoch presents some serious challenges. Perhaps one of the most important unknowns in reionisation studies is the nature of the sources responsible for the ionising photons. A likely candidate are stellar sources in galaxies. However, their contribution heavily depends on the fraction of produced photons that can make it out of the galaxy, the so-called escape fraction. I will present different ways in which we have tried to constrain the escape fraction at high redshift. Using detailed models of isolated disc galaxies at high redshift we found that the local gas complexes that give rise to star formation are the main constraint for the escape of radiation. I then compare these results to a large sample of galaxies extracted from a cosmological simulation of galaxy formation. Finally, I will discuss a set of exotic starburst galaxies that were recently observed in the local Universe, and what we can learn from them about escape fractions at high redshift.