compact high-velocity clouds (CHVCs)
abrhâ-ye hampak-e tondrow
Fr.: nuages compacts à grande vitesse
A population of relatively small (typically < 2°) → high-velocity clouds, which are spatially and kinematically isolated from the gas distribution in their environment. They are thought to be located in the → intergalactic medium of the → Local Group.
high-velocity clouds (HVCs)
Fr.: nuages à grande vitesse
A population of neutral or partly ionized gas clouds in the → Galactic halo which are seen as high-altitude structures in the atomic hydrogen 21 cm emission at high radial velocities (vLSR> 100 km/sec). They have substantial neutral column densities (> 1019 cm-2) and their metallicities range from 0.1 to about 1.0 times solar. The distances to the majority of them remain unknown. They may represent the continuing infall of matter onto the → Local Group. See also → compact high-velocity clouds.