2001A&A...375..219B

Growing evidence supports the suggestion that the compact high-velocity clouds of Hi (CHVCs) are located throughout the Local Group and continue to fuel galactic evolution. Recent distance estimates to individual objects lie in the range 150-850 kpc, implying an Hi mass range of 10^5.7->10^7.2M_☉ together with sizes ranging from 2-12kpc, while the average linewidth is 30km/s FWHM. It is natural to ask whether objects of this type would not already have been seen by current blind Hi surveys of the extragalactic sky. We consider the properties of the deepest published surveys of this type and conclude that the sensitivity and coverage have now begun to reveal the high mass end of the distribution (M_HI>10⁷M_☉). Achieving detection limits an order of magnitude deeper should finally enable direct study of these systems beyond the Local Group, or definitively rule out their existence.