CHVCs: Galactic Building Blocks at z = 0

Abstract

A distinct sub-class of anomalous velocity HI emission features has emerged from recent high quality surveys of the Local Group environment, namely the compact high velocity clouds (CHVCs). A program of high-resolution imaging with the Westerbork array and the Arecibo telescope has begun to provide many insights into the nature of these objects. Elongated core components with a velocity gradient consistent with rotation (V_Rot ~ 15 km/s) are seen in many objects. Comparison of volume and column densities has allowed the first distance estimates to be made (600+/-300 kpc). The objects appear to be strongly dark-matter dominated with dark-to-gas mass ratios of 30-50 implied if the typical distance is 700 kpc.