Origin of Non-axisymmetric Features of Virgo Cluster Early-type Dwarf
  Galaxies. II. Tidal Effects on Disk Features and Stability
  A fraction of dwarf galaxies in the Virgo cluster contain disk features like
bars and spiral arms. Using $N$-body simulations, we investigate the effects of
tidal forces on the formation of such disk features in disk dwarf galaxies
resembling VCC856. We consider 8 Cluster-Galaxy models in which disk dwarf
galaxies with differing pericenter distance and spin orientation experience the
tidal gravitational force of a Virgo-like NFW halo, and additional 8
Galaxy-Galaxy models in which two dwarf galaxies undergo tidal interactions
with different strength. We find that the cluster tidal effect is moderate due
to the small galaxy size, making the bars form earlier by $\sim1$--$1.5\Gyr$
compared to the cases in isolation. While the galactic halos significantly lose
their mass within the virial radius due to the cluster tidal force, the mass of
the stellar disks is nearly unchanged, suggesting that the inner regions of a
disk-halo system is secured from the tidal force. The tidal forcing from either
the cluster potential or a companion galaxy triggers the formation of two-armed
spirals at early time before a bar develops. The tidally-driven arms decay and
wind with time, suggesting that they are kinematic density waves. In terms of
the strength and pitch angle, the faint arms in VCC856 are best matched with
the arms in a marginally unstable galaxy produced by a distant tidal encounter
with its neighbor $\sim0.85\Gyr$ ago.
