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Paper: HI SNRs, FV Wings, and the Structure of the ISM
Volume: 323, Star Formation in the Interstellar Medium: In Honor of David Hollenbach, Chris McKee, and Frank Shu
Page: 123
Authors: Koo, B.-C.
Abstract: We discuss the statistics of old supernova remnants (SNRs) with expanding HI shells, or "HI SNRs", in the Galaxy. Systematic HI 21-cm emission line studies have detected fast-moving atomic gas associated with 25 SNRs, which is about 10% of the known radio/X-ray SNRs. This number is much less than the expected number of visible HI SNRs if the interstellar medium is filled with warm neutral medium. A plausible explanation is that most of the HI SNRs are too faint to be visible in radio or X-ray. Large-scale (l, v) diagrams of the Hi 21-cm emission in the Galactic plane show broad wings which extend to velocities forbidden by the Galactic rotation. Many of these "forbidden-velocity (FV)" wings are not associated with known SNRs or known external galaxies and could be candidates for heretofore unidentified old HI SNRs. We discuss the properties of the FV wings and the implications for the structure of the interstellar medium.
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