UCHVC (Ultra-compact High Velocity Cloud) survey

The paucity of low mass galaxies in the Universe is a long-standing

problem. We recently presented a set of isolated ultra-compact high

velocity clouds (UCHVCs) identified within the dataset of the Arecibo

Legacy Fast ALFA (ALFALFA) HI line survey that are consistent with

representing low mass gas-bearing dark matter halos within the Local

Group (Adams et al. 2013). At distances of ~1 Mpc, the UCHVCs have HI

masses of ~10^5 Msun and indicative dynamical masses of ~10^7

Msun. The HI diameters of the UCHVCs range from 4' to 20', or 1 to 6

kpc at a distance of 1 Mpc. We have selected the most compact and

isolated UCHVCs with the highest average column densities as

representing the best galaxy candidates. Several of these systems have

been observed with WSRT to enable higher spatial resolution (~40-60")

studies of the HI distribution. The HI morphology revealed by the WSRT

data offers clues to the environment of the UCHVCs, and velocity

fields allow the underlying mass distribution to be constrained. I

will present initial results comparing the observed HI distribution to

theoretical models of gas in low mass dark matter halos. I will also

highlight the discovery of Leo P as a HI detection in the ALFALFA

survey.