A blind HI survey of the M81 group

Results are presented of the first blind H I survey of the M81 Group of gal axies. The data were taken as part of the H I Jodrell All-Sky Survey (HIJAS S). The survey reveals several new aspects to the complex morphology of the H I distribution in the group. All four of the known dwarf irregular (dIrr ) galaxies close to M81 can be unambiguously seen in the HIJASS data. Each forms part of the complex tidal structure in the area. We suggest that at l east three of these galaxies may have formed recently from the tidal debris in which they are embedded. The structure connecting M81 to NGC 2976 is re vealed as a single tidal bridge of mass similar or equal to2.1 x 10(8) M-. projected spatial extent similar or equal to 80 kpc. Two "spurs" of H I pro jecting from the M81 complex to lower declinations are traced over a consid erably larger spatial and velocity extent than by previous surveys. The dwa rf elliptical (dE) galaxies BK5N and Kar 64 lie at the spatial extremity of one of these features and appear to be associated with it. We suggest that these may be the remnants of dIrr's that have been stripped of gas and tra nsmuted into dE's by close gravitational encounters with NGC 3077. The nucl eated dE galaxy Kar 61 is unambiguously detected in H I for the first time and has an H I mass of similar to 10(8) M-., further confirming it as a dE/ dIrr transitional, object. HIJASS has revealed one new possible group membe r, HIJASS J1021+6842. This object contains similar or equal to2 x 10(7) M-. of H I and lies similar or equal to 105' from IC 2574. It has no optical c ounterpart on the Digital Sky Survey.