DYNAMICAL FRICTION IN HEAD-ON GALAXY COLLISIONS .2. N-BODY SIMULATIONS OF RADIAL AND NONRADIAL ENCOUNTERS

This is the second article of a series devoted to the dynamical study of nearly radial collisions between an elliptical galaxy and a small s atellite. We here present a set of restricted and full N-body simulati ons which complement our analytical work (Seguin & Dupraz 1994) and em phasise the role played by the various parameters of the collision. Us ing a ''Particle-Mesh'' code, we follow the orbital decay of the satel lite in the course of the collision and show that the two processes re sponsible for the accretion - dynamical friction and tidal stripping - have a concurrent rather than complementary influence on the sinking satellite. Shell formation around the elliptical is discussed in the l ight of this competition. Special attention is paid to highly eccentri c collisions. Our results indicate that dynamical friction is much les s sensitive to the value of the impact parameter than tidal forces. If the core of the satellite is to survive and merge with the galaxy, th e optimal configuration involves a compact dwarf on a slightly non-rad ial encounter. We also stress the inadequacy of Chandrasekhar's formul a as an empirical description of dynamical friction along head-on enco unters. In contrast with the circular case, the phenomenon is dominate d by the transient nature of the galactic response. This and some astr ophysical implications will be discussed in a forthcoming article (Seg uin & Dupraz 1995, in preparation).