THE HEAD-ON COLLISION BETWEEN 2 GAS-RICH GALAXIES - NEUTRAL HYDROGEN DEBRIS FROM THE CENTRALLY SMOOTH RING GALAXY VII-ZW-466

We present VLA observations of the distribution and kinematics of the PI I gas in the classical ring galaxy VII Zw 466 and its immediate sur roundings. The H I gas corresponding to the bright optical star formin g ring exhibits the typical profile of a rotating-expanding ring. The systemic velocity of the galaxy is found to be 14,468 +/- 25 km s(-1). A formal fit to the H I kinematics in the ring is consistent with bot h ring rotation and expansion (expansion velocity 32 km s(-1)). Howeve r, H I in the northeast quadrant of the ring is severely disturbed, sh owing evidence of tidal interaction. In addition, fingers of H I gas e xtend from the galaxy to the east in the general direction of the two major companions. We also detect a hydrogen plume from the southern ed ge-on companion galaxy (G2) pointing toward the ring galaxy. This, and other peculiarities associated with G2 suggest that it is the intrude r galaxy which recently collided with VII Zw 466 and formed the ring. Numerical hydrodynamic models are presented that show that most of the observed features can be accounted for as a result of the impact spla sh between two gas disks. The resultant debris is stretched by ring wa ve motion in the bridge and later forms accretion streams onto the two galaxies. Finally, we detect H I emission from two previously unknown dwarf galaxies located northeast and southeast of VII Zw 466, respect ively. This brings the total number of members of the VII Zw 466 group to five. Using the projected mass method, the upper limit of the dyna mical mass of the group was estimated to be M(0) = 3.5 x 10(12) M(circ le dot), which implies that the mass-to-light ratio of the group is (M /L)(group) approximate to 70. This rather low value of M/L, as compare d with other loose groups, suggests the group may be in a state of col lapse at the present time. Plunging orbits would naturally lead to an enhanced probability of head-on collisions and ring galaxy formation.