A Blind H [CSC]i[/CSC] Survey of the M81 Group

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Abstract
Results are presented of the first blind H I survey of the M81 Group of galaxies. The data were taken as part of the H I Jodrell All-Sky Survey (HIJASS). 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 least 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 revealed as a single tidal bridge of mass 2.1 × 108 M☉ and projected spatial extent 80 kpc. Two "spurs" of H I projecting from the M81 complex to lower declinations are traced over a considerably larger spatial and velocity extent than by previous surveys. The dwarf 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 transmuted into dE's by close gravitational encounters with NGC 3077. The nucleated dE galaxy Kar 61 is unambiguously detected in H I for the first time and has an H I mass of ~108 M☉, further confirming it as a dE/dIrr transitional object. HIJASS has revealed one new possible group member, HIJASS J1021+6842. This object contains 2 × 107 M☉ of H I and lies 105' from IC 2574. It has no optical counterpart on the Digital Sky Survey.
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