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J. S. Gallagher (U. Wisconsin-Madison)
Low mass disk galaxies, the irregulars and related systems, combine gas-rich environments and low gravitational binding energies with occasional episodes of intense star formation. These types of galaxies also tend to be relatively transparent to ionizing radiation and thus show bright extra-HII region diffuse ionized gas (DIG) features. This combination of circumstances aids the production and visibility of large scale structures in the ISM; these galaxies are excellent places in which to explore interactions between massive stars and their surroundings. An important aspect of these phenomena are how they vary with scale. We therefore consider a sequence of structures, beginning with simple shells produced by low energy events associated with normal modes of star formation, and extending up to major starbursts which disturb entire galaxies. In following this sequence we can estimate what conditions are required for the time and spatial coherence of star formation to account for observed ionized structures, and thereby gain insights into the operation of feedback processes on galactic scales.
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