A Simulation Based Inference Approach to the Dynamics of the MW–LMC System - Validation

Abstract The infall of the LMC into the Milky Way (MW) has generated dynamical disequilibrium throughout the MW. The interaction has displaced the MW’s centre of mass, manifesting as an apparent ‘reflex motion’ in velocities of outer halo stars. Often, expensive high fidelity MW–LMC simulations are required to model these effects, though the range of model parameter spaces can be large and complex. We investigate the ability of lower fidelity, rigid MW–LMC simulations to reliably infer the model parameters of higher fidelity N-body and hydrodynamical cosmological zoom-in MW–LMC simulations using a Simulation Based Inference (SBI) approach. We produce and release a set of 128,000 MW–LMC rigid potentials, with stellar haloes evolved to present-day, each adopting a unique combination of model parameters including the MW mass, the LMC mass and the dynamical friction strength. For these simulation parameters, we use SBI to find their posterior distributions. We find that our SBI framework trained on rigid MW–LMC simulations is able to correctly infer the true simulation LMC mass within a 1σ confidence interval from both N-body and cosmological simulations when knowledge of the induced MW reflex motion is provided as data. This motivates future applications of the presented SBI framework to observational data, which will help constrain both MW and LMC properties, as well as the dynamics of the MW’s reflex motion.