Dynamical Friction in Cuspidal Galaxies

Dynamical friction is the process responsible for matter transport toward the inner regions of galaxies in form of massive objects, like intermediate mass black holes, globular clusters and small satellite galaxies. While very bright galaxies show an almost flat luminosity profile in the inner region, fainter ones have, usually, a peaked, cuspidal, profile toward the center. This makes unreliable, in these cases, the use of the classic Chandrasekhar's formula for dynamical friction in its local approximation. Using both N-body simulations and a semi analytical approach, we have obtained reliable results for the orbital decay of massive objects in cuspidal galaxies. A relevant result is that of a shallower dependence of dynamical friction braking on the satellite mass than in the usual Chandrasekhar's local expression, at least in a range of large satellite masses.