THE INTERACTION BETWEEN SPIRAL GALAXIES IC-2163 AND NGC-2207 .2. MODELS

Observations of the disturbed morphologies and internal velocity distr ibutions, and of the relative positions, orientations, and centroid ve locities of the interacting spiral galaxies IC 2163 and NGC 2207, are reproduced by computer simulations of each galaxy. The ocular morpholo gy of IC 2163, consisting of a bright oval with pointed apices and a d ouble-parallel structure in the tidal arm, as well as the streaming mo tions along the oval and the arms and the nearly perpendicular alignme nt of the kinematic and photometric minor axes, are fitted to a model in which IC 2163 is reacting to an in-plane, prograde encounter with N GC 2207 that had a closest approach similar to 4 x 10(7) yr ago. In NG C 2207, strong velocity anomalies consisting of a global distortion of the velocity distribution into an S shape and a 40 degrees misalignme nt of the kinematic and photometric minor axes are fitted by a dynamic al model in which the companion, IC 2163, moved in a plane perpendicul ar to the disk of NGC 2207 with the same relative orbit as in the IC 2 163 model. The resulting out-of-plane tidal forces are producing a war p of the disk of NGC 2207 with present z-displacements as large as 9 k pc and present z-velocities up to 100 km s(-1). The large southern ext ension of NGC 2207 observed in H I and in optical images is probably a tidal remnant from the time, similar to 2.4 x 10(8) yr ago, when IC 2 163 crossed the western extrapolated plane of NGC 2207 from the near s ide to the far side, prior to perigalacticon on the far side. The high resolution of both the observations and the models gives an unprecede nted view of the dynamics of strong tidal interactions between galaxie s.