Modeling the dynamical friction timescale of a sinking satellite

Abstract

When a satellite galaxy falls into a massive dark matter halo, it suffers from the dynamical friction force which drags it into the halo's center, where it finally merges with the central galaxy. The time interval between entry and merger is called the dynamical friction timescale (Tdf ). Many studies have been dedicated to deriving Tdf using analytical models or N-body simulations. These studies have obtained qualitative agreements on how Tdf depends on the orbital parameters, and the mass ratio between the satellite and the host's halo. However, there are still disagreements on deriving an accurate form for Tdf . We present a semi-analytical model to predict Tdf and we focus on interpreting the discrepancies among different studies. We find that the treatment of mass loss from the satellite by tidal stripping dominates the behavior of Tdf . We also identify other model parameters which affect the predicted Tdf.