EVIDENCE FOR AN INTERACTION IN THE NEAREST STARBURSTING DWARF IRREGULAR GALAXY IC 10

Using deep 21 cm H i data from the Green Bank Telescope we have detected an ≳18.3 kpc long gaseous extension associated with the starbursting dwarf galaxy IC 10. The newly found feature stretches 1.°3 to the northwest and has a large radial velocity gradient reaching to ∼65 km s−1 lower than the IC 10 systemic velocity. A region of higher column density at the end of the extension that possesses a coherent velocity gradient (∼10 km s−1 across ∼26′) transverse to the extension suggests rotation and may be a satellite galaxy of IC 10. The H i mass of IC 10 is 9.5 × 107 (d/805 kpc)2 M☉ and the mass of the new extension is 7.1 × 105 (d/805 kpc)2 M☉. An IC 10–M31 orbit using known radial velocity and proper motion values for IC 10 show that the H i extension is inconsistent with the trailing portion of the orbit so that an M31–tidal or ram pressure origin seems unlikely. We argue that the most plausible explanation for the new feature is that it is the result of a recent interaction (and possible late merger) with another dwarf galaxy. This interaction could not only have triggered the origin of the recent starburst in IC 10, but could also explain the existence of previously found counter-rotating H i gas in the periphery of the IC 10 which was interpreted as originating from primordial gas infall.