Simulating the evolution of disc galaxies in a group environment. I. The
  influence of the global tidal field
  We present the results of a series of numerical simulations aimed to study
the evolution of a disc galaxy within the global tidal field of a group
environment. Both the disc galaxy and the group are modelled as
multi-component, collision-less, N-body systems, composed by both dark matter
and stars. In our simulations, the evolution of disc galaxies is followed as
their orbits sink towards the group centre, under the effect of dynamical
friction. We explore a broad parameter space, covering several aspects of the
galaxy-group interaction that are potentially relevant to galaxy evolution.
Namely, prograde and retrograde orbits, orbital eccentricities, disc
inclination, role of a central bulge in discs, internal disc kinematics, and
galaxy-to-group mass ratios. We find that significant disc transformations
occur only after the mean density of the group, measured within the orbit of
the galaxy, exceeds ~0.3-1 times the central mean density of the galaxy. The
morphological evolution of discs is found to be strongly dependent on the
initial inclination of the disc with respect to its orbital plane. That is,
discs on face-on and retrograde orbits are shown to retain longer their disc
structures and kinematics, in comparison to prograde discs. This suggests that
after interacting with the global tidal field alone, a significant fraction of
disc galaxies should be found in the central regions of groups. Prominent
central bulges are not produced, and pre-existing bulges are not enhanced in
discs after the interaction with the group. Assuming that most S0 are formed in
group environments, this implies that prominent bulges should be formed mostly
by young stars, created only after a galaxy has been accreted by a group.
Finally, contrary to some current implementations of tidal stripping in
semi-analytical models of galaxy evolution, we find that more massive galaxies
suffer more tidal stripping.
