Astronomy and Astrophysics – Astrophysics – Galaxy Astrophysics
Scientific paper
2011-06-23
Astronomy and Astrophysics
Astrophysics
Galaxy Astrophysics
To appear in MNRAS, 26 pages, 7 figures, single column v2 - Small changes to reflect published version, fixed y-axis scaling o
Scientific paper
We study the force of dynamical friction acting on a gravitating point mass that travels through an extended, isothermal gas. This force is well established in the hypersonic limit, but remains less understood in the subsonic regime. Using perturbation theory, we analyze the changes in gas velocity and density far from the mass. We show analytically that the steady-state friction force is Mdot*V, where Mdot is the mass accretion rate onto an object moving at speed V. It follows that the speed of an object experiencing no other forces declines as the inverse square of its mass. Using a modified version of the classic Bondi-Hoyle interpolation formula for Mdot as a function of V, we derive an analytic expression for the friction force. This expression also holds when mass accretion is thwarted, e.g. by a wind, as long as the wind-cloud interaction is sufficiently confined spatially. Our result should find application in a number of astrophysical settings, such as the motion of galaxies through intracluster gas.
Lee Aaron T.
Stahler Steven W.
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