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