Astrophysics, abstract
astro-ph/0601490

From: X. Hernandez [view email]

Date: Sat, 21 Jan 2006 00:40:05 GMT (87kb)

An extensive study of dynamical friction in dwarf galaxies: the role of stars, dark matter, halo profiles and MOND

Authors: F.J. Sanchez-Salcedo, Jorge Reyes-Iturbide, X. Hernandez

Comments: 17 pages, three figures, submitted to MNRAS

We investigate the dynamical friction in-spiraling timescales of globular clusters in dwarf galaxies (dSph and dE), exploring various possibilities for their gravitational make up. We address the problem of these timescales having been variously estimated in the literature as much shorter than a Hubble time. Under the assumption of a dark halo having a constant density central core with a typical radius somewhat larger than the observed stellar core radius, dynamical friction timescales are naturally extended upwards of a Hubble time. The above when carefully considering dynamical friction in a self consistent two component system, the observed stellar distribution, and a dark matter component constrained by measured stellar velocity dispersions, both of which contribute to the dynamical drag. Galactic dark halos having a cuspy central structure yield timescales $\lesssim$ 4.5 Gyr, for any dark halo parameters in accordance with observations of dwarf stellar velocity dispersion. We confirm, after a detailed formulation of the dynamical friction problem under the alternative hypothesis of MOND dynamics and in the lack of any dark matter, that due to the enhanced dynamical drag of the stars themselves, the dynamical friction timescales in MOND would be extremely short. Taking the well measured structural parameters of the Fornax dSph and its globular cluster system as a case study, we conclude that requiring dynamical friction timescales comparable to the Hubble time strongly favours a model where the observed stellar kinematics are determined by equilibrium within a dark matter halo having a core.

http://arxiv.org/abs/astro-ph/0601490