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Paper: HI Shells in the Milky Way
Volume: 331, Extra-Planar Gas
Page: 67
Authors: Ehlerova, S.; Palous, J.
Abstract: We study properties of HI shells in the second quadrant of the MilkyWay and their connection to HII regions. We use a catalog of HI shells created by the automatic identification algorithm HOLMES applied to the Leiden- Dwingeloo HI survey. The catalog contains nearly 300 shells in the second quadrant. Their average angular dimension is 5°, the average expansion velocity 8 km s−1 and the flattening Δbt ≈ 0.8. Dimensions of shells at low-z coordinates (z ≤ 1 kpc) are not different from shells at high z-coordinates, but the high-z shells are more elongated than their low-z counterparts. We also study the connection between HI shells and HII regions and find that their longitudinal distributions match. We give an example of a connection between an HI shell and an HII region NGC 7538.

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