Evolution induced by dry minor mergers onto fast-rotator S0 galaxies
  We analysed collisionless N-body simulations of intermediate and minor dry
mergers onto S0s to test whether these mergers can generate S0 galaxies with
kinematics intermediate between fast and slow rotators. We find that minor
mergers induce a lower decrease of the global rotational support than
encounters of lower mass ratios, which results in S0s with properties
intermediate between fast and slow rotators. The resulting remnants are
intrinsically more triaxial, less flattened, and span the whole range of
apparent ellipticities up to $\epsilon_\mathrm{e} \sim 0.8$. They do not show
lower apparent ellipticities in random projections than initially; on the
contrary, the formation of oval distortions and the disc thickening increase
the percentage of projections at $0.4 < \epsilon_\mathrm{e} < 0.7$. In the
experiments with S0b progenitor galaxies, minor mergers tend to spin up the
bulge and to decrease slightly its intrinsic ellipticity, whereas in the cases
of primary S0c galaxies they keep the rotational support of the bulge nearly
constant and decrease significantly its intrinsic ellipticity. The remnant
bulges remain nearly spherical ($B/A \sim C/A > 0.9$), but exhibit a wide range
of triaxialities ($0.20 < T < 1.00$). In the plane of global anisotropy of
velocities ($\delta$) vs. intrinsic ellipticity ($\epsilon_\mathrm{e,intr}$),
some of our models extend the linear trend found in previous major merger
simulations towards higher $\epsilon_\mathrm{e,intr}$ values, while others
depart from it. This is consistent with the wide dispersion exhibited by real
S0s in this diagram compared with ellipticals, which follow the linear trend
drawn by major merger simulations. The different trends exhibited by
ellipticals and S0 galaxies in the $\delta$ - $\epsilon_\mathrm{e}$ diagram may
be pointing to the different role played by major mergers in the build-up of
each morphological type.
