A. Feldmeier-Krause, T Maindl, G. van de Ven, S. Thater, P. Jethwa, I. P. Breda
Abstract
Context. The centre of the Milky Way is occupied by a dense nuclear star cluster that contains the supermassive black hole Sgr A⋆. The mildly flattened cluster is embedded in the larger surrounding nuclear stellar disc. These three components dominate the mass budget of the Galactic centre at different radial scales. Aims. The mass distribution of the Galactic centre has been studied extensively using observations of individual bright stars and various dynamical modelling approaches. The situation differs for external galaxies, where observations are often limited to the integrated line-of-sight kinematics. For such systems, triaxial orbit-based dynamical modelling has become a standard method of deriving mass distributions and stellar orbit distributions. We aim to apply and test this method on the Galactic centre. Methods. We extracted stellar line-of-sight kinematic maps of the inner ~3 pc×66 pc region of the Galactic centre. We used the DYNAMITE code, which calculates an orbit library in a given gravitational potential and computes model kinematic maps. These model maps were then compared to the observed kinematic maps, and thus the gravitational potential and orbit distribution of the Galactic centre were constrained. Results. We recover the correct mass of Sgr A⋆, and our stellar mass distributions are in agreement with the literature, albeit with larger uncertainties. We find that the stellar structures are at most mildly triaxial and close to oblate. The contribution of dark matter to the total mass distribution is of the order of <1%. The stellar orbit distribution in the inner ~33 pc region is dominated by dynamically warm and hot orbits. At larger scales of ~80─160 pc, dynamically cold ─ highly rotating ─ orbits have the largest weights. Conclusions. The dominance of hot and warm orbits is a consequence of short dynamical timescales in the inner Galactic centre, causing dynamical heating of the orbits. The presence of cold orbits at large radii may be explained by the longer heating timescales in this region, and by the stars in the outer nuclear stellar disc being younger. The agreement of our mass distribution with other studies confirms the validity of the orbit-based modelling approach.
Keywords
Galaxy: center / Galaxy: kinematics and dynamics
Astronomy & Astrophysics
Volume 711, Article Number A98, Number of pages 16
2026 July
