A sensitive high-velocity HI survey

Extract

The observational studies of the neutral hydrogen high velocity clouds (HVC's) in the last decade have for the most part concentrated on the detailed study of the prominent complexes discovered by the surveys of the late 1960's. More recently, several HVC's were discovered, often by accident, with very high velocities, which are typically outside of the velocity range and below the sensitivity limit of the old surveys. The tendency to associate these clouds with the closest galaxy at hand became a rather common practice. The idea that the Local Group, or the Local Supercluster, is populated with such “intergalactic clouds” was fed by these discoveries, and generalized to the whole field of the HVC's. I have repeatedly argued against the latter generalization (Giovanelli 1977, 1978). In this paper I shall report on the progress of a new survey that intends to constitute a test of the intergalactic approach itself.