The resonant nature of tidal stirring of disky dwarf galaxies orbiting
  the Milky Way
  Using N-body simulations we study the tidal evolution of initially disky
dwarf galaxies orbiting a Milky Way-like host, a process known to lead to the
formation of dwarf spheroidal galaxies. We focus on the effect of the
orientation of the dwarf galaxy disk's angular momentum with respect to the
orbital one and find very strong dependence of the evolution on this parameter.
We consider four different orientations: the exactly prograde, the exactly
retrograde and two intermediate ones. Tidal evolution is strongest for the
exactly prograde and weakest for the exactly retrograde orbit. In the prograde
case the stellar component forms a strong bar and remains prolate until the end
of the simulation, while its rotation is very quickly replaced by random
motions of the stars. In the retrograde case the dwarf remains oblate, does not
form a bar and loses rotation very slowly. In the two cases of intermediate
orientation of the disk, the evolution is between the two extremes, suggesting
a monotonic dependence on the inclination. We interpret the results in terms of
the resonance between the angular velocity of the stars in the dwarf and its
orbital motion by comparing the measurements from simulations to semi-analytic
predictions. We conclude that resonant effects are the most important mechanism
underlying the tidal evolution of disky dwarf galaxies.
