High-Velocity Clouds and Galactic Evolution
High-velocity clouds (HVCs) are HI clouds deviating strongly from the general Galactic rotation. Their distances, and hence origins, have long remained unknown. However, three major complexes are now known to lie at z > 1 kpc, while two smaller clouds are closer to the plane (Wakker et al. 1995). These incomplete results still allow a variety of origins.