Does the Giant HII Region SMC-N66 Leak Ionizing Photons?

SMC-N66 is a giant HII region associated with the NGC 346 young stellar complex in the Small Magellanic Cloud. The ionized gas in N66 has a diffuse structure with few well-defined ionization edges. Using archival HST and ground-based data, we created an Halpha emission intensity map and found a non-uniform, extended distribution that shows gaps and holes within the ionized region. Our analysis suggests that there are areas where the high-energy ionizing photons could be escaping from the nebula. Current estimates for the production of ionizing photons from massive stars relative to the ionization rate in N66 indicate that Lyman continuum photons may be escaping, although a final answer depends on better knowledge of the effects of dust extinction and the stellar Lyman continuum fluxes. This work was supported by the National Science Foundation’s REU program in Astrophysics through NSF award AST-1852136.