Motion of halo tracer objects in the gravitational potential of a low-mass model of the Galaxy

¹ Astronomical Observatory, Jagiellonian University, Orla 171, 30244 Kraków, Poland
e-mail: Lukasz.Bratek@ifj.edu.pl
² Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskego 152, 31342 Kraków, Poland
³ Institute of Physics, Jagiellonian University, Reymonta 4, 30059 Kraków, Poland

Received: 26 March 2015
Accepted: 26 May 2015

Abstract

Recently, we determined a lower bound for the Milky Way mass in a point mass approximation. We obtain this result for most general spherically symmetric phase-space distribution functions consistent with a measured radial velocity dispersion. As a stability test of these predictions against a perturbation of the point mass potential, in this paper we make use of a representative of these functions to set the initial conditions for a simulation in a more realistic potential of similar mass and to account for other observations. The predicted radial velocity dispersion profile evolves to forms still consistent with the measured profile, proving structural stability of the point mass approximation and the reliability of the resulting mass estimate of ~2.1 × 10¹¹ M_⊙ within 150 kpc. As a byproduct, we derive a formula in the spherical symmetry relating the radial velocity dispersion profile to a directly measured kinematical observable.