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Paper: Large Scale Structures in the Interstellar Medium
Volume: 352, New Horizons in Astronomy: Frank N. Bash Symposium 2005
Page: 95
Authors: McClure-Griffiths, N.M.
Abstract: Galactic interstellar medium (ISM) studies have undergone a renaissance in the past ten years due in part to new large-scale surveys of the Galactic ISM. New surveys of neutral hydrogen (H I), in particular the Canadian and Southern Galactic Plane Surveys, excel because of their exceptional spatial dynamic range, combining single-dish and interferometer data for arcminute resolution imaging over areas of many degrees. These surveys are allowing us to probe the physics of the global ISM in more detail than ever before. Among the largest and most energetic discrete objects observed in the ISM are H I supershells and chimneys. These objects play a pivotal, though not fully understood, role in the Galactic ecosystem. They heat and reshape the ISM on scales of parsecs to hundreds of parsecs and are a significant source of structure and energy input into the ISM. H I supershells also provide convenient locations for energy dissipation on small scales. For example, instabilities that develop along the dense swept-up walls may be sites of cooling and molecular cloud formation. Understanding this transition from the hot-ionized gas presumably filling the interior of shells, to the warm neutral medium of the outer walls, to the cold neutral medium along the small-scale instability-created features, and finally to the molecular gas is crucial to understanding the evolution of the ISM. In this review I show some examples of the detailed observations possible of large-scale supershells and also discuss their role in the interaction of the Galactic disk with the halo.
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