The origin of prolate rotation in dwarf spheroidal galaxies formed by
  mergers of disky dwarfs
  Motivated by the discovery of prolate rotation of stars in Andromeda II, a
dwarf spheroidal companion of M31, we study its origin via mergers of disky
dwarf galaxies. We simulate merger events between two identical dwarfs changing
the initial inclination of their disks with respect to the orbit and the amount
of orbital angular momentum. On radial orbits the amount of prolate rotation in
the merger remnants correlates strongly with the inclination of the disks and
is well understood as due to the conservation of the angular momentum component
of the disks along the merger axis. For non-radial orbits prolate rotation may
still be produced if the orbital angular momentum is initially not much larger
than the intrinsic angular momentum of the disks. The orbital structure of the
remnants with significant rotation is dominated by box orbits in the center and
long-axis tubes in the outer parts. The frequency analysis of stellar orbits in
the plane perpendicular to the major axis reveals the presence of two families
roughly corresponding to inner and outer long-axis tubes. The fraction of inner
tubes is largest in the remnant forming from disks oriented most vertically
initially and is responsible for the boxy shape of the galaxy. We conclude that
prolate rotation results from mergers with a variety of initial conditions and
no fine tuning is necessary to reproduce this feature. We compare the
properties of our merger remnants to those of dwarfs resulting from the tidal
stirring scenario and the data for Andromeda II.
