Dynamical friction of bodies orbiting in a gaseous sphere |
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| Authors: | F J Sánchez-Salcedo † A Brandenburg † |
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| Institution: | Department of Mathematics, University of Newcastle, Newcastle upon Tyne NE1 7RU;Nordita, Blegdamsvej 17, DK 2100 Copenhagen Ø, Denmark |
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| Abstract: | The dynamical friction experienced by a body moving in a gaseous medium is different from the friction in the case of a collisionless stellar system. Here we consider the orbital evolution of a gravitational perturber inside a gaseous sphere using three-dimensional simulations, ignoring however self-gravity. The results are analysed in terms of a 'local' formula with the associated Coulomb logarithm taken as a free parameter. For forced circular orbits, the asymptotic value of the component of the drag force in the direction of the velocity is a slowly varying function of the Mach number in the range 1.0–1.6. The dynamical friction time-scale for free decay orbits is typically only half as long as in the case of a collisionless background, which is in agreement with E. C. Ostriker's recent analytic result. The orbital decay rate is rather insensitive to the past history of the perturber. It is shown that, similarly to the case of stellar systems, orbits are not subject to any significant circularization. However, the dynamical friction time-scales are found to increase with increasing orbital eccentricity for the Plummer model, whilst no strong dependence on the initial eccentricity is found for the isothermal sphere. |
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| Keywords: | hydrodynamics waves galaxies: clusters: general galaxies: kinematics and dynamics galaxies: star clusters |
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