Charting galactic accelerations II: how to 'learn' accelerations in the solar neighbourhood

Abstract

Gravitational acceleration fields can be deduced from the collisionless Boltzmann equation, once the distribution function is known. This can be constructed via the method of normalizing flows from datasets of the positions and velocities of stars. Here, we consider application of this technique to the solar neighbourhood. We construct mock data from a linear superposition of multiple `quasi-isothermal' distribution functions, representing stellar populations in the equilibrium Milky Way disc. We show that given a mock dataset comprising a million stars within 1 kpc of the Sun, the underlying acceleration field can be measured with excellent, sub-percent level accuracy, even in the face of realistic errors and missing line-of-sight velocities. The effects of disequilibrium can lead to bias in the inferred acceleration field. This can be diagnosed by the presence of a phase space spiral, which can be extracted simply and cleanly from the learned distribution function. We carry out a comparison with two other popular methods of finding the local acceleration field (Jeans analysis and 1D distribution function fitting). We show our method most accurately measures accelerations from a given mock dataset, particularly in the presence of disequilibria.

13 pages (inc. 2 appendices), 6 figures. Submitted to MNRAS. All code, plotting scripts etc available at https://github.com/aneeshnaik/LocalFlows

References in corpus (13)

• galpy: A Python Library for Galactic Dynamics
• The Local Dark Matter Density
• Stellar Abundances in the Solar Neighborhood: The Hypatia Catalog
• Distances and parallax bias in Gaia DR2
• Origin and evolution of moving groups I. Characterization in the observational kinematic-age-metallicity space
• Measuring the local dark matter density with LAMOST DR5 and Gaia DR2
• A Number of Nearby Moving Groups may be Fragments of Dissolving Open Clusters
• The Milky Way Tomography with SDSS. V. Mapping the Dark Matter Halo
• Galactoseismology and the Local Density of Dark Matter
• The Stellar Distribution Function and Local Vertical Potential from Gaia DR2
• Kinematic modelling of clusters with Gaia: the Death Throes of the Hyades
• Weighing the Galactic disk in sub-regions of the solar neighbourhood using Gaia DR2
• Charting Galactic Accelerations: When and How to Extract a Unique Potential from the Distribution Function