Milky Way mass models for orbit calculations

¹ Dr. Karl Remeis-Observatory & ECAP, Astronomical Institute, Friedrich-Alexander University Erlangen-Nuremberg, Sternwartstr. 7, 96049 Bamberg, Germany
e-mail: andreas.irrgang@sternwarte.uni-erlangen.de
² School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, KY16 9SS, UK
³ Department of Physics, University of Arizona, Tucson, AZ 85721, USA
⁴ Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Received: 11 October 2012
Accepted: 16 November 2012

Abstract

Context. Studying the trajectories of objects like stars, globular clusters, or satellite galaxies in the Milky Way allows the dark matter halo to be traced but requires reliable models of its gravitational potential.

Aims. Realistic, yet simple and fully analytical, models have already been presented in the past. However, improved, as well as new, observational constraints have become available in the meantime, calling for a recalibration of the respective model parameters.

Methods. Three widely used model potentials are revisited. By a simultaneous least-squares fit to the observed rotation curve, in-plane proper motion of Sgr A*, local mass/surface density, and the velocity dispersion in Baade’s window, parameters of the potentials are brought up-to-date. The mass at large radii – in particular, that of the dark matter halo – is hereby constrained by requiring that the most extreme known halo, blue horizontal-branch star has to be bound to the Milky Way.

Results. The Galactic mass models are tuned to yield a very good match to recent observations. The mass of the dark matter halo is – within the limitations of the applied models – estimated in a fully consistent way. As a first application, the trajectory of the hypervelocity star HE 0437-5439 is investigated again to check its suggested origin in the Large Magellanic Cloud (LMC).

Conclusions. Despite their simplicity, the presented Milky Way mass models are very able to reproduce all observational constraints. Their analytical and simple form makes them ideally suited for fast and accurate orbit calculations. The LMC cannot be ruled out as HE 0437-5439’s birthplace.