## 6. Conclusions and discussionIn Sect. 2 of this work we showed in a quantitative way how
the collapse time of a shell of baryonic matter
made of galaxies and substructure depends on some parameters. When one
of the parameters or or
increases, the collapse time grows. It means
that the effects of the presence of dynamical friction should be more
evident in the outer regions of rich clusters of galaxies. Besides, we
show how the collapse time of an infalling shell increases with
decreasing values of , and becomes very large
for Mpc (see Fig. 4). As a consequence,
the slowing down of the collapse of an outer shell within a cluster of
galaxies owing to the dynamical friction is more remarkable in the
clusters with nucleus of little dimension. In Sect. 3 of this paper we give an analytical relation that
links the dimensionless collapse time with the
coefficient of dynamical friction . This
relation is in excellent agreement with the numerical integration of
Eq. (7) for (see Fig. 5). Then, we
find an analytical relation between and the
parameters on which it depends for the value
(we remind that the effects of the dynamical friction are negligible
for ). This is Eq. (28), that can be
considered as a © European Southern Observatory (ESO) 1998 Online publication: May 15, 1998 |