On the Efficiency of the Tidal Stirring Mechanism for the Origin of
  Dwarf Spheroidals: Dependence on the Orbital and Structural Parameters of the
  Progenitor Disky Dwarfs
  (Abridged) The tidal stirring model posits the formation of dSph galaxies via
the tidal interactions between rotationally-supported dwarfs and MW-sized host
galaxies. Using a set of collisionless N-body simulations, we investigate the
efficiency of the tidal stirring mechanism. We explore a wide variety of dwarf
orbital configurations and initial structures and demonstrate that in most
cases the disky dwarfs experience significant mass loss and their stellar
components undergo a dramatic morphological and dynamical transformation: from
disks to bars and finally to pressure-supported spheroidal systems with
kinematic and structural properties akin to those of the classic dSphs in the
Local Group (LG). Our results suggest that such tidal transformations should be
common occurrences within the currently favored cosmological paradigm and
highlight the key factor responsible for an effective metamorphosis to be the
strength of the tidal shocks at the pericenters of the orbit. We demonstrate
that the combination of short orbital times and small pericenters,
characteristic of dwarfs being accreted at high redshift, induces the strongest
transformations. Our models also indicate that the transformation efficiency is
affected significantly by the structure of the progenitor disky dwarfs. Lastly,
we find that the dwarf remnants satisfy the relation Vmax = \sqrt{3} * sigma,
where sigma is the 1D, central stellar velocity dispersion and Vmax is the
maximum halo circular velocity, with intriguing implications for the missing
satellites problem. Overall, we conclude that the action of tidal forces from
the hosts constitutes a crucial evolutionary mechanism for shaping the nature
of dwarf galaxies in environments such as that of the LG. Environmental
processes of this type should thus be included as ingredients in models of
dwarf galaxy formation and evolution.
