| Abstract | The VLA D-Array was used to determine the distribution and kinematics of the atomic hydrogen in the interacting galaxy pair NGC 7714/7715 (Arp 284). The H I gas peaks near the center of NGC 7714 and surrounds both optical galaxies, extending to a maximum radius of 6'(~71 kpc) to the southwest. There is an H I bridge between the two galaxies, coincident with the stellar bridge, and an H I tail associated with the long western optical tail of NGC 7715. The velocity field across NGC 7714 shows the classical signature of an inclined rotating disk, with deviations from circular motion near the ends of the NGC 7714 tails. Using a restricted 3-body dynamical model, we have constructed a likely formation scenario for NGC 7714/7715. The morphology and kinematics of this system are reproduced successfully with a parabolic off-center collision (impact parameter r_min_~ 0.85 times the radius of the disk) between two unequal-mass disk galaxies (M_2_/M_1_ ~ 0.3), where the companion passes through the main galaxy on a retrograde orbit inclined ~30^deg^ from the perpendicular. From this model, we estimate that the inclination angle for NGC 7714 is ~30^deg^, and ~1.1 x 10^8^ yr have passed since the point of closest approach. The large impact parameter may explain why no star formation is observed in the NGC 7714 ring, in contrast with most ring galaxies; the star formation morphology in NGC 7714 may be governed by bar dynamics rather than by the expanding density wave mechanism thought to occur in more central collisions. For the central starburst in NGC 7714, a comparison of the dynamical mass and the current star formation rate indicates that either the initial mass function (IMF) in NGC 7714 is skewed to high-mass stars or the age of the NGC 7714 starburst is significantly less than the dynamical age of the interaction If the IMF is similar to that in the solar neighborhood, there has been a time delay between the point of closest approach and the initiation of central star formation, consistent with theoretical models of interaction-triggered nuclear starbursts. |
