Australia Telescope National Facility

Faint, discrete HI clouds near the Galactic plane have recently been observed using the Green Bank Telescope (Lockman, 2002). Distances to these clouds can be determined by looking towards tangent points of the inner Galaxy at velocities expected from Galactic rotation. This provides a huge advantage over most HI clouds by allowing us to determine their physical properties such as size and mass. The GASS data are being used to create a complete inventory of such clouds, along with a statistical evaluation of their physical properties. Figure 1 shows that these clouds are quite abundant and may be responsible for a considerable amount of HI mass in the lower halo.

GASS provides sensitive, high angular and spectral resolution data for studying the nature and origin of HVCs. Work is underway to provide an updated catalog of high and intermediate velocity clouds (HVCs and IVCs), searching in particular for narrow line clouds and those close to Galactic velocities that would have been missed in previous catalogs. These clouds will be studied for information about their physical and spectral structure.