Galactic Mass Estimates using Dwarf Galaxies as Kinematic Tracers

TL;DR

This paper employs a hierarchical Bayesian approach with dwarf galaxy kinematic data to estimate the Milky Way's mass profile, incorporating prior information and analyzing the influence of the Large Magellanic Cloud.

Contribution

It introduces a new Bayesian hierarchical model for Milky Way mass estimation using dwarf galaxy data, integrating prior info from simulations and past studies.

Findings

Median mass within 200 kpc: 1.19×10^{12} M_⊙

Mass estimates align with recent studies using Gaia data

Evidence suggests some dwarf galaxies are affected by the LMC

Abstract

New mass estimates and cumulative mass profiles with Bayesian credible regions (c.r.) for the Milky Way (MW) are found using the Galactic Mass Estimator (GME) code and dwarf galaxy (DG) kinematic data from multiple sources. GME takes a hierarchical Bayesian approach to simultaneously estimate the true positions and velocities of the DGs, their velocity anisotropy, and the model parameters for the Galaxy's total gravitational potential. In this study, we incorporate meaningful prior information from past studies and simulations. The prior distributions for the physical model are informed by the results of Eadie & Juric (2019), which used globular clusters instead of DGs, as well as by the subhalo distributions of the Ananke Gaia-like surveys from Feedback In Realistic Environments-2 (Fire-2) cosmological simulations (see Sanderson et al. 2020). Using DGs beyond 45 kpc, we report median and 95% c.r estimates for $r_{200}$ = 212.8 (191.12,238.44) kpc, and for the total enclosed mass $M_{200}$ = 1.19 (0.87,1.68)$\times10^{12}M_{\odot}$ (adopting $\Delta_c=200$). Median mass estimates at specific radii are also reported (e.g., $M(<50\text{ kpc})=0.52\times10^{12}M_{\odot}$ and $M(100\text{ kpc})=0.78\times10^{12}M_{\odot}$). Estimates are comparable to other recent studies using GAIA DR2 and DGs, but notably different from the estimates of Eadie & Juric (2019). We perform a sensitivity analysis to investigate whether individual DGs and/or a more massive Large Magellanic Cloud (LMC) on the order of $10^{11}M_{\odot}$ may be affecting our mass estimates. We find possible supporting evidence for the idea that some DGs are affected by a massive LMC and are not in equilibrium with the MW.