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Motivated by the discovery of prolate rotation of stars in Andromeda II, adwarf spheroidal companion of M31, we study its origin via mergers of diskydwarf galaxies. We simulate merger events between two identical dwarfs changingthe initial inclination of their disks with respect to the orbit and the amountof orbital angular momentum. On radial orbits the amount of prolate rotation inthe merger remnants correlates strongly with the inclination of the disks andis well understood as due to the conservation of the angular momentum componentof the disks along the merger axis. For non-radial orbits prolate rotation maystill be produced if the orbital angular momentum is initially not much largerthan the intrinsic angular momentum of the disks. The orbital structure of theremnants with significant rotation is dominated by box orbits in the center andlong-axis tubes in the outer parts. The frequency analysis of stellar orbits inthe plane perpendicular to the major axis reveals the presence of two familiesroughly corresponding to inner and outer long-axis tubes. The fraction of innertubes is largest in the remnant forming from disks oriented most verticallyinitially and is responsible for the boxy shape of the galaxy. We conclude thatprolate rotation results from mergers with a variety of initial conditions andno fine tuning is necessary to reproduce this feature. We compare theproperties of our merger remnants to those of dwarfs resulting from the tidalstirring scenario and the data for Andromeda II.

The origin of prolate rotation in dwarf spheroidal galaxies formed by mergers of disky dwarfs