A Milky Way with a massive, centrally concentrated thick disc: new Galactic mass models for orbit computations

TL;DR

This paper introduces two new Galactic mass models including a massive thick disc, which significantly affect orbital calculations of stars and globular clusters, highlighting the importance of thick disc considerations.

Contribution

The paper presents novel axisymmetric Galactic mass models with a massive thick disc, improving orbit computations and observational consistency.

Findings

Orbital parameters can vary by 30-40% due to thick disc presence.

Systematic uncertainties in the rotation curve affect orbital calculations.

Models satisfy key observational constraints.

Abstract

In this work, two new axisymmetric models for the Galactic mass distribution are presented. Motivated by recent results, these two models include the contribution of a stellar thin disc and of a thick disc, as massive as the thin counterpart but with a shorter scale-length. Both models satisfy a number of observational constraints: stellar densities at the solar vicinity, thin and thick disc scale lengths and heights, rotation curve(s), and the absolute value of the perpendicular force Kz as a function of distance to the Galactic centre. We numerically integrate into these new models the motion of all Galactic globular clusters for which distances, proper motions, and radial velocities are available, and the orbits of about one thousand stars in the solar vicinity. The retrieved orbital characteristics are compared to those obtained by integrating the clusters and stellar orbits in pure thin disc models. We find that, due to the possible presence of a thick disc, the computed orbital parameters of disc stars can vary by as much as 30-40%. We also show that the systematic uncertainties that affect the rotation curve still plague computed orbital parameters of globular clusters by similar amounts.