v 1 1 0 Fe b 19 97 Atomic Hydrogen and Star Formation in the Bridge / Ring Interacting

We present high spatial resolution 21 cm HI maps of the interacting galaxy pair NGC 7714/7715. We detect a massive (2 × 109M⊙) HI bridge connecting the galaxies that is parallel to but offset from the stellar bridge. A chain of HII regions traces the gaseous bridge, with Hα peaks near but not on the HI maxima. An HI tidal tail is also detected to the east of the smaller galaxy NGC 7715, similarly offset from a stellar tail. The strong partial stellar ring on the east side of NGC 7714 has no HI counterpart, but on the opposite side of NGC 7714 there is a 109M⊙ HI loop ∼ 11 kpc in radius. Within the NGC 7714 disk, clumpy HI gas is observed associated with star formation regions. Redshifted HI absorption is detected towards the strong starburst nucleus. We compare the observed morphology and gas kinematics with gas dynamical models in which a low-mass companion has an off-center prograde collision with the outer disk of a larger galaxy. These simulations suggest that the bridge in NGC 7714/7715 is a hybrid between the tidal bridges seen in systems like M51 and the purely gaseous ‘splash’ bridges found in ring galaxies like the Cartwheel. The offset between the stars and gas in the bridge may be due to dissipative cloud-cloud collisions occuring during the impact of the two gaseous disks. Subject headings: galaxies: individual (NGC 7714/7715) galaxies: interactions galaxies: kinematics and dynamics radio lines: atomic