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D.A. Thilker (NMSU)
The interstellar medium is filled with superbubbles resulting from the "violent" interaction between massive stars and their gaseous environment. Strong stellar winds and supernovae inject copious kinetic energy resulting in bulk supershell motion. Furthermore, substantial thermal energy content is known to be present in hot gas filling the HI bubbles. Stochastic self-propagating star formation is also commonly observed on the periphery of giant HI supershells. For these reasons, understanding supershell properties is vital in the context of galactic evolution models.
We have developed an automated object recognition software package to enable systematic detection and study of supershell populations in a large number of spiral galaxies. Thilker, Braun, and Walterbos (1998) first demonstrated this technique for NGC2403. Mashchenko, Thilker, and Braun (1998) later refined the procedure, incorporating realistic projected supershell models during the data analysis. We now present results and discussion for a more extensive sample of nearby galaxies.
Our work indicates a correlation between the global rate of star formation (SFR) and the total kinetic energy of supershells in a galaxy. We also discuss the observed supershell size distribution, making comparison with the theoretical predictions of Oey & Clarke (1997). Bubbles which break out of the disk can provide an effective conduit for enriched gas moving into the halo of a galaxy. We estimate the magnitude of this flow based on the total observed number of such shells. Finally, it appears that galaxy-wide measurements of dispersion in the 21-cm line profile may be largely attributable to the expansion of superbubbles distributed throughout the disk.
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