Dynamical friction against the perturber mass M, for V = 1.5c_T = 0, with the results from finite-time linear perturbation theory included with dotted lines of the same colors. The departure from perturbation theory for the zero-temperature case at high M is due to nonlinear effects. Increasing the mass of the perturber causes the superfluid to behave increasingly like a normal fluid, similarly to the effect of decreasing .