"The Local Universe in Neutral Hydrogen"

Recent blind 21-cm surveys of the nearby universe reveal for the first time an unbiased view of the cold neutral hydrogen component in the local universe. These surveys include all sky surveys and surveys focused on the ``Zone of Avoidance''; the region of the extragalactic sky which is largely obscured in optical wavelengths by Milky Way dust.

HI surveys of the Zone of Avoidance can fill in the currently incomplete knowledge of the local distribution of galaxies and, assuming galaxies trace mass, the local gravity field. Zone of Avoidance and all-sky surveys can determine the HI content of the local universe and may help in selecting between galaxy formation and evolution models. For instance, are the low-mass, high velocity clouds remnants of the formation of the local group, and is there a similar gas-rich, but low surface brightness component in galaxy groups and in voids which has been missed in optical surveys?