Radiative feedback in galaxies

We examine the fate of ionizing radiation from massive stars on global scales. First, we compare the observed H luminosities of LMC Hii regions with those predicted by the latest generation of stellar atmosphere models. Our results imply that classical Hii regions are on average radiation-bounded, rather than density-bounded, as we found a decade ago. This is likely to necessitate an additional ionizing source for the diffuse, warm ionized medium (WIM) in galaxies. Secondly, we present new results from the SINGG H galaxy survey, showing that starburst galaxies have a lower fraction of WIM emission than normal star-forming galaxies. The most intriguing and consequential possible cause for this effect is the escape of ionizing radiation from starbursts. We show that the observations are also consistent with our predictions for the escape of ionizing radiation. Nevertheless, other observations do not necessarily support this scenario and other possible explanations must be considered.