Shades and Apparitions: Toward an Inventory of Cold Hydrogen Clouds

With the Phase I CGPS now complete at 21cm, we are in a position to examine the population of cold H I clouds over the entire range of the survey. Current methods of H I self-absorption (HISA) identification and analysis allow us to explore the properties and distribution of the portion of cold H I which appears as HISA shadows in the 21cm line data. Such studies are necessarily biased toward clouds with bright background emission. However, the same software algorithms used to locate HISA can also be inverted to locate narrow-line H I emission. The results of complementary HISA and ``negative HISA'' searches are presented and discussed.