  For a rigid model satellite, Chandrasekhar's dynamical friction formula
describes the orbital evolution quite accurately, when the Coulomb logarithm is
chosen appropriately. However, it is not known if the orbital evolution of a
real satellite with the internal degree of freedom can be described by the
dynamical friction formula. We performed N-body simulation of the orbital
evolution of a self-consistent satellite galaxy within a self-consistent parent
galaxy. We found that the orbital decay of the simulated satellite is
significantly faster than the estimate from the dynamical friction formula. The
main cause of this discrepancy is that the stars stripped out of the satellite
are still close to the satellite, and increase the drag force on the satellite
through two mechanisms. One is the direct drag force from particles in the
trailing tidal arm, a non-axisymmetric force that slows the satellite down. The
other is the indirect effect that is caused by the particles remaining close to
the satellite after escape. The force from them enhances the wake caused in the
parent galaxy by dynamical friction, and this larger wake in turn slows the
satellite down more than expected from the contribution of its bound mass. We
found these two have comparable effects, and the combined effect can be as
large as 20% of the total drag force on the satellite.
