Detecting dark matter in high-velocity clouds

Many high-velocity H I clouds (HVCs) are now believed to be scattered throu ghout the Galactic halo on scales of tens of kiloparsecs. Some of these clo uds appear to contain substantial H I masses (> 10(6) M.). It has been sugg ested that these structures may be associated with dark matter "minihalos" accreting onto the Galactic halo. For a compact HVC along the sight line to a more distant galaxy, we demonstrate that "pixel gravitational lensing" p rovides a crucial test for the presence of a dark halo in the form of massi ve compact objects. The detection of pixel lensing will provide an independ ent means of mapping the mass distribution within HVCs.