Physical Properties of Tidal Features of Interacting Disk Galaxies:
  Three-dimensional Self-consistent Models
  Using self-consistent three-dimensional (3D) N-body simulations, we
investigate the physical properties of non-axisymmetric features in a disk
galaxy created by a tidal interaction with its companion. The primary galaxy
consists of a stellar disk, a bugle, and a live halo, corresponding to
Milky-Way type galaxies, while the companion is represented by a halo alone. We
vary the companion mass and the pericenter distance to explore situations with
differing tidal strength parameterized by either the relative tidal force P or
the relative imparted momentum S. We find that the formation of a tidal tail in
the outer parts requires P > 0.05 or S > 0.07. A stronger interaction results
in a stronger, less wound tail that forms earlier. Similarly, a stronger tidal
forcing produces stronger, more loosely wound spiral arms in the inner parts.
The arms are approximately logarithmic in shape, with both amplitude and pitch
angle decaying with time. The derived pattern speed decreases with radius and
is close to the Omega-kappa/2 curve at late time, with Omega and kappa denoting
the angular and epicycle frequencies, respectively. This suggests that the
tidally-induced spiral arms are most likely kinematic density waves weakly
modified by self-gravity. Compared to the razor-thin counterparts, arms in the
3D models are weaker, have a smaller pitch angle, and wind and decay more
rapidly. The 3D density structure of the arms is well described by the
concentrated and sinusoidal models when the arms are in the nonlinear and
linear regimes, respectively. We demonstrate that dynamical friction between
interacting galaxies transfers the orbital angular momentum of one galaxy to
the spin angular momentum of the companion halo.
