A SIMULATION ATLAS OF TIDAL FEATURES IN GALAXIES

Detailed simulations of tidally induced structure in disk galaxies hav e either concentrated on specific systems or consisted of a few encoun ters with relatively small numbers of particles and no self-gravity. O bservers need a ''dictionary'' of simulations that covers many encount er parameters with fine morphological resolution and includes effects of self-gravitation. Observers can then search the dictionary for the parameters that best match a particular observed morphology. Alternati vely, the dictionary can be used with observational samples for statis tical studies of system parameters. To fill this need, we present a su rvey of model tidal encounters using a self-gravitating, 180,000 parti cle, two-component (''stars'' and ps'') disk. A wide variety of fascin ating morphologies results. There are 86 different encounters that var y orbit tilt, perigalacticon distance, galaxy to companion mass ratio, and the amount of halo dark matter relative to the disk. For morpholo gical comparisons, over 1700 images of the entire survey are available in video form. While there is a rich variety of tidal structure cover ing much of this parameter space, some general patterns may be remarke d. There is a strong orbital inclination dependence of the symmetry of tidal patterns, most symmetric for planar orbits and nearly one-sided for polar encounters. Retrograde encounters produce only broad fanlik e global patterns, but rich small-scale internal structure. In both ki nds of encounter, our numerical resolution allows us to track internal spiral structure driven by the outer material arms, especially in the lighter halo simulations. We note also that polar encounters generate series of expanding, essentially non-rotating loops resembling shell structures in some respects.