Orbit-superposition models of discrete, incomplete stellar kinematics: application to the Galactic centre

Journal article

We present a method for fitting orbit-superposition ("Schwarzschild") models to the kinematics of discrete stellar systems when the available stellar sample is not complete, but has been filtered by a known selection function. As an example, we apply it to Fritz et al.'s kinematics of the innermost regions of the Milky Way's nuclear stellar cluster. Assuming spherical symmetry, our models fit a black hole of mass $M_\bullet=(3.76\pm0.22)\times10^6\,M_\odot$, surrounded by an extended mass $M_\star=(6.57\pm0.54)\times10^6\,M_\odot$ within 4 parsec. The best-fitting mass models have an approximate power-law density cusp $\rho\propto r^{-\gamma}$ within 1 parsec, with $\gamma=1.3\pm0.3$. We carry out an extensive investigation of how our modelling assumptions might bias these estimates: $M_\bullet$ is the most robust parameter and $\gamma$ the least. Internally the best-fitting models have broadly isotropic orbit distributions, apart from a bias towards circular orbits between 0.1 and 0.3 parsec.

Authors: Magorrian, J

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 484
• Issue: 1
• Pages: 1166–1181
• Publication date: 2019-01-07
• Acceptance date: 2019-01-01
• DOI: 10.1093/mnras/stz037
• EISSN: 1365-2966
• ISSN: 0035-8711
• Keywords: astro-ph.GA