The Jeans modeling of the Milky Way galaxy: implications of the kinematics of the stellar halo

Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia
e-mail: srdjan@aob.bg.ac.rs; ana@aob.bg.ac.rs

Received: 17 March 2011
Accepted: 28 April 2011

Abstract

Aims. We investigate the predictions of Newtonian dynamics and the MOND theory related to the Milky Way galaxy using the Jeans equation.

Methods. We used the measurements of the radial velocities of the blue horizontal branch (BHB) halo stars to test the predictions of Newtonian gravity and to also extend our study to different MOND models, taking orbital anisotropies that we calculate into account.

Results. The halo stars of the Galaxy were used as a tracer of the Galaxy’s gravitational potential. The Jeans equation was calculated for both the Newtonian and the MOND approaches. We assumed spherical symmetry and calculated the Jeans equation by taking orbital anisotropies into account. Circular velocities for both approaches were also analyzed.

Conclusions. We solved the Jeans equation in spherical approximation and confirm that the Newtonian model without dark matter cannot fit the observed velocity dispersion profile and that the truncated flat model with dark matter can provide a good fit to the observed velocity dispersion. For the MOND models, from the Jeans modeling and the models of the circular velocity curves, we found that two models can provide a fit to the data without significant anisotropies whereas two other tested models need various anisotropies to obtain the same result.