The following document lists the file abstract/WWALLER_M33_GHRS.abs
from catalogue VI/111.
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Resolution of nearby giant HII regions (GHRs) into their stellar and nebular constituents provides fundamental insights for interpreting more distant and powerful starburst activity. At a distance of 0.84 Mpc, M33 is the closest galaxy which contains a large number of GHRs of differing metallicity and luminosity. As such, M33 provides the ideal laboratory for investigating the degree to which metallicity and environment affect the stellar and nebular properties of starbursting systems. We have obtained HST/WFPC2 images of 6 GHRs in M33. These multi-band images clearly resolve the underlying stellar populations down to a linear scale of 0.4 pc. Complementary groundbased imaging at H-alpha, [SII], and other emission lines reveal disturbed morphologies and strong excitation gradients in the ionized gas. Photometric analysis of the resolved stellar populations indicate a puzzling shortfall of ionizing luminosity relative to the gaseous ionization. What could be providing the additional ionization? We propose to address this question by imaging the IR line emission and continua from these starburst nebulae. The many fine-structure emission lines in the IR spectrum span a wide range of ionization energies, thereby providing well-resolved diagnostics of the radiative and mechanical (shock) energetics at work in the nebulae. They are also not subject to extinction like those measured in the visible. The distribution of continuum emission from the entrained dust grains will further constrain the fraction of ionizing radiation that is absorbed and thus removed from the ionization budget. The combined dataset will be unparalleled in its comprehensive and detailed coverage of GHRs, thereby providing a solid foundation for diagnosing the composite stellar and nebular emission from more distant galaxian starbursts.