Milky Way mass models for orbit calculations

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.

On the accuracy of close stellar approaches determination

“…Our study is based on the best available data in the pre-Gaia era, mainly from the HIP2 (van Leeuwen 2011) and XHIP (Anderson & Francis 2012) catalogues. We used a numerical integration in the rectilinear, Galactocentric coordinates taking into account the full gravitational potential of the Galaxy in its modern shape (Irrgang et al 2013). For the main purpose (the accuracy assessment) we utilised covariance matrices of astrometric data which is included in the HIP2 catalogue.…”

“…Numerical parameters for this model are taken from Irrgang et al (2013) and are summarised in Table 1. Since we always numerically integrate these equations simultaneously for a star and the Sun (to present final, heliocentric results), we also account for the gravitational attraction between these two bodies, as they can approach arbitrarily close. Our test calculation shows that the greatest influence of taking into account Sun-star gravitational interaction is for star HIP 26744.…”

Estimates of black hole natal kick velocities from observations of low-mass X-ray binaries

“…Therefore, we do not expect the uncertainty in the Galactic potential to significant impact our findings. We use the three models presented in (Irrgang et al 2013), all of which fit the observed data well, to estimate that uncertainty in the 1 Under the most optimistic assumptions, H 1705-250 may have been born near its present location in (ρ, z), making a black-hole birth kick unnecessary; however this appears relatively unlikely given the present-day massive-star formation.…”

Clues on the missing sources of reionization from self-consistent modelling of Milky Way and dwarf galaxy globular clusters

“…Data for the Milky GCs is from Georgiev et al (2009a), data for M31 is from Strader et al (2011) and data for GCs in local dwarf galaxies is from Georgiev et al (2009b). The mass model we use for the Milky way is from Irrgang et al (2013).…”