Free-floating HI clouds in the M 81 group

Recent VLA observations pointed at dwarf spheroidal (dSph) galaxies in the M 81 group reveal a hitherto hidden population of extremely low mass (~ 10 ⁵ M) HI clouds with no obvious optical counterparts. We have searched 10 fields in the M 81 group totalling 2.2 square degree, both targeting known dwarf spheroidal galaxies and blank fields around the central triplet. Our observations show that the new population of lowmass HI clouds appears to be confined to a region toward the southeast of the central triplet (at distances of ~ 100 kpc from M 81). Possible explanations for these freefloating HI clouds are that they are related to the dSphs found to the SouthEast of M 81, that they belong to the galaxies of the M 81 triplet (equivalent to HVCs), that they are of primordial nature and provide fresh, unenriched material falling into the M 81 group, or that they are tidal debris from the 3body interaction involving M 81M 82NGC 3077. Based on circumstantial evidence, we currently favour the latter explanation.