| Author(s): | Just, A., Peñarrubia, J. |
| Title: | Dynamical friction in Inhomogeneous Systems |
| Source: | submitted to Astron. Astrophys. |
| Year: | 2002 |
| Abstract: | Dynamical friction plays an important role in the orbital evolution of massive objects in a sea of lighter particles (satellite galaxies in Dark Matter haloes, Super-massive Black Holes in galaxy centres, massive stars in star clusters). The standard formula of Chandrasekhar based locally on an isotropic and homogeneous distribution function worked in the past surprisingly well. But in the last years, due to the improved numerical facilities, systematic deviations were observed. In recent work, three aspects of improvements are discussed: Variation of the Coulomb logarithm with position along the orbit, anisotropic velocity distribution functions, and the effect of the local density gradient. In this paper we discuss the effect of a position dependent Coulomb logarithm and the influence of the local density gradient on the dynamical friction force. We apply the new formulae to the orbital evolution of satellite galaxies in the Dark Matter halo. We compare semi-analytical computations with numerical N-body calculations for the analysis of the different approaches to the dynamical friction formula. We find that for a maximum impact parameter proportional to the local scale length, there is a significant improvement of the orbital fit and reduction of the circularisation of the orbit as is observed in most numerical calculations. The additional force due to the density gradient contributes up to 10% to the total friction force, but shows a completely different behaviour. The net effect on the orbital evolution is very small in the first tests. We expect a significant effect on the circularisation and precession rate of the orbits for more eccentric orbits and larger masses of the massive object relative to the enclosed background mass. |
| Preprint issued: | December 2002 |
| Remarks: |
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Letzte Änderung/Updated: 02.08.2004