  We investigate properties of material ejected dynamically in the merger of
black hole-neutron star binaries by numerical-relativity simulations. We
systematically study the dependence of ejecta properties on the mass ratio of
the binary, spin of the black hole, and equation of state of the neutron-star
matter. Dynamical mass ejection is driven primarily by tidal torque, and the
ejecta is much more anisotropic than that from binary neutron star mergers. In
particular, the dynamical ejecta is concentrated around the orbital plane with
a half opening angle of 10--20deg and often sweeps out only a half of the
plane. The ejecta mass can be as large as ~0.1M_sun, and the velocity is
subrelativistic with ~0.2--0.3c for typical cases. The ratio of the ejecta mass
to the bound mass (disk and fallback components) is larger, and the ejecta
velocity is larger, for larger values of the binary mass ratio, i.e., for
larger values of the black-hole mass. The remnant black hole-disk system
receives a kick velocity of O(100)km/s due to the ejecta linear momentum, and
this easily dominates the kick velocity due to gravitational radiation.
Structures of postmerger material, velocity distribution of the dynamical
ejecta, fallback rates, and gravitational waves are also investigated. We also
discuss the effect of ejecta anisotropy on electromagnetic counterparts,
specifically a macronova/kilonova and synchrotron radio emission, developing
analytic models.
