Physical parameters of two Compact High-Velocity Clouds Structure, dynamics and possible origin

nature is discussed controversially until today. HVCs are gas clouds, in which the baryonic matter consists mainly of neutral atomic hydrogen. They have radial velocities, which are not consistent with a simple galactic rotation model. Both the origin and the spatial distribution of the HVCs are still unknown. The main reason for this is the difficulty to determine the distance of HVCs. A subclass of the HVCs are the so-called Compact High-Velocity Clouds (CHVCs), which were identified by Braun & Burton in 1999. CHVCs are defined by their small angular diameter of < 2 ° FWHM. They are spatially and kinematically isolated from the gas distribution in their environment. ö The basis of our analysis are the Parkes and ATCA 21-cm data of two CHVCs (HVC 297+09+253 and HVC 291+26+195), which were observed by Br ns et al. (2005) in the framework of an HI survey of the Magellanic System. The velocity resolution of the Parkes data is 1 km/s and for theATCAdata 0.8 km/s. The observations of the two clouds with a single-dish telescope on the one hand and with an interferometer on the other hand makes it possible to analyze the total HI masses and the extended structures as well as the small-scale structures within the clouds.