Abstract
We present the results of a search for faint H I 21 cm emission line at velocities forbidden by Galactic rotation in the Galactic plane using the Leiden/Dwingeloo H I Survey data and the H I Southern Galactic Plane Survey data. These forbidden-velocity wings (FVWs) appear as protruding excessive emission in comparison with their surroundings in limited (2°) spatial regions over velocity extents of more than ~20 km s-1 in large-scale (l, v) diagrams. Their high velocities imply that there should be some dynamical phenomena associated. We have identified 87 FVWs. We present their catalog and discuss their distribution and statistical properties. We found that 85% of FVWs are not coincident with known supernova remnants (SNRs), galaxies, or high-velocity clouds. Their natures are currently unknown. We suspect that many of them are fast-moving H I shells and filaments associated with the oldest SNRs that are essentially invisible except via their H I line emission. We discuss other possible origins.
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