Slow evolution of quasi-collisionless systems of stars induced by dynamical friction on a minority population of heavier objects

The main goal of our investigation is to set up a numerical laboratory for the study of the slow evolution of an otherwise collisionless stellar system, as a result of the interactions with a minority component of heavier objects. The effects that we would like to study are those attributed to slow collisional relaxation and generally called ``dynamical friction''. We start by revisiting the problem of the sinking of a single satellite inside an initially isotropic, non-rotating, spherical galaxy, which we follow by means of N-body simulations using about one million particles. We then consider a quasi-spherical problem, in which the satellite is fragmented into a set of many smaller masses with a spherically symmetric initial density distribution. In a wide set of experiments, designed in order to bring out effects genuinely associated with dynamical friction, we have been able to demonstrate the slow evolution of the density profile, the development of a tangentially biased pressure, and other significant phenomena in phase space for the underlying stellar system.