Dynamical friction in cuspy galaxies

TL;DR

This paper investigates the decay of massive objects due to dynamical friction in cuspy galaxies, introducing a semi-analytical method that outperforms traditional approximations and reveals higher friction efficiency in such environments.

Contribution

It presents a new semi-analytical approach for dynamical friction in cuspy galaxies, validated against N-body simulations, and highlights differences from classical models.

Findings

Semi-analytical method matches N-body results within 1%

Dynamical friction is more efficient in cuspy galaxies

Decay time scales as M^-0.67, shallower than 1/M

Abstract

In this paper we treat the problem of the dynamical friction decay of a massive object moving in an elliptical galaxy with a cuspidal inner distribution of the mass density. We present results obtained by both self-consistent, direct summation, N-body simulations, as well as by a new semi-analytical treatment of dynamical friction valid in such cuspy central regions of galaxies. A comparison of these results indicates that the proposed semi-analytical approximation is the only reliable in cuspy galactic central regions, where the standard Chandrasekhar's local approximation fails, and, also, gives estimates of decay times that are correct at 1% respect to those given by N-body simulations. The efficiency of dynamical friction in cuspy galaxies is found definitively higher than in core galaxies, especially on more radially elongated satellite orbits. As another relevant result, we find a proportionality of the dynamical friction decay time to the -0.67 power of the satellite mass, M, shallower than the standardly adopted 1/M dependence.