Weighing the Galactic disk using phase-space spirals IV. Tests on a three-dimensional galaxy simulation

TL;DR

This study validates a phase-space spiral method for measuring the Galactic disk's gravitational potential using a complex 3D galaxy simulation, demonstrating robustness against perturbations and selection effects.

Contribution

It tests and confirms the accuracy of a novel method for estimating the Galactic disk's mass distribution in a realistic, perturbed galaxy simulation.

Findings

Method yields unbiased gravitational potential estimates with 7% error.

Robust against severe, unknown selection effects.

Effective in complex, disturbed galaxy environments.

Abstract

In this fourth article on weighing the Galactic disk using the shape of the phase-space spiral, we have tested our method on a billion particle three-dimensional N-body simulation, comprised of a Milky Way like host galaxy and a merging dwarf satellite. The main purpose of this work was to test the validity of our model's fundamental assumptions that the spiral inhabits a locally static and vertically separable gravitational potential. These assumptions might be compromised in the complex kinematic system of a disturbed three-dimensional disk galaxy; in fact, the statistical uncertainty and any potential biases related to these assumptions are expected to be amplified for this simulation, which differs from the Milky Way in that it is more strongly perturbed and has a phase-space spiral that inhabits higher vertical energies. We constructed 44 separate data samples from different spatial locations in the simulated host galaxy. Our method produced accurate results for the vertical gravitational potential of these 44 data samples, with an unbiased distribution of errors with a standard deviation of 7 %. We also tested our method under severe and unknown spatially dependent selection effects, also with robust results; this sets it apart from traditional dynamical mass measurements that are based on the assumption of a steady state and which are highly sensitive to unknown or poorly modelled incompleteness. Hence, we will be able to make localised mass measurements of distant regions in the Milky Way disk, which would otherwise be compromised by complex and poorly understood selection effects.