Milky Way Mass Models for Orbit Calculations

TL;DR

This paper updates simple analytical models of the Milky Way's gravitational potential using recent observational data, enabling accurate orbit calculations and re-evaluating the origin of a hypervelocity star.

Contribution

It recalibrates three widely used Milky Way mass models with new data, improving their accuracy for orbit calculations and dark matter halo mass estimation.

Findings

Updated Milky Way mass models fit recent observations.

Dark matter halo mass constrained by stellar binding criteria.

LMC remains a plausible origin for hypervelocity star HE 0437-5439.

Abstract

Studying the trajectories of objects like stars, globular clusters or satellite galaxies in the Milky Way allows to trace the dark matter halo but requires reliable models of its gravitational potential. 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. Three widely used model potentials are revisited. By a simultaneous least-squared 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 - and thus in particular that of the dark matter halo - is hereby constrained by imposing that the most extreme halo blue horizontal-branch star known has to be bound to the Milky Way. 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 re-investigated to check its suggested origin in the Large Magellanic Cloud (LMC). Despite their simplicity, the presented Milky Way mass models are well 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.