Radiative Feedback in Galaxies

344 Greenlow Road, Catonsville, MD 21228, U.S.A.Abstract.We examine the fate of ionizing radiation from massive stars on global scales. First, wecompare the observed Hα luminosities of LMC Hii regions with those predicted by the latestgeneration of stellar atmosphere models. Our results imply that classical Hii regions are onaverage radiation-bounded, rather than density-bounded, as we found a decade ago. This islikely to necessitate an additional ionizing source for the diffuse, warm ionized medium (WIM)in galaxies. Secondly, we present new results from the SINGG Hα galaxy survey, showing thatstarburst galaxies have a lower fraction of WIM emission than normal star-forming galaxies. Themost intriguing and consequential possible cause for this effect is the escape of ionizing radiationfrom starbursts. We show that the observations are also consistent with our predictions for theescape of ionizing radiation. Nevertheless, other observations do not necessarily support thisscenario and other possible explanations must be considered.Keywords. stars: atmospheres, stars: early-type, galaxies: evolution, galaxies: ISM, galaxies:starburst, Hii regions, intergalactic medium, Magellanic Clouds