Simulating the evolution of disc galaxies in a group environment. II.
  The influence of close-encounters between galaxies
  We study the evolution of disc galaxies in group environments under the
effect of both the global tidal field and close-encounters between galaxies,
using controlled N-body simulations of isolated mergers. We find that
close-range encounters between galaxies are less frequent and less damaging to
disc galaxies than originally expected, since they mostly occur when group
members have lost a significant fraction of their initial mass to tidal
stripping. We also find that group members mostly affect disc galaxies
indirectly by modifying their common global tidal field. Different initial
orbital parameters of group members introduce a significant "scatter" in the
evolution of general properties of disc galaxies around a "median" evolution
that is similar to when only the effect of the global tidal field is included.
Close-encounters introduce a high variability in the properties of disc
galaxies, even slowing their evolution in some cases, and could wash out
correlations between galaxy properties and the group total mass. The combined
effect of the global tidal field and close-encounters appears to be inefficient
at forming/enhancing central stellar bulges. This implies that bulges of S0
galaxies should be mostly composed by young stars, which is consistent with
recent observations.
