OTI on FIRE: Testing the Efficacy of Orbital Torus Imaging to Recover the Galactic Potential

TL;DR

This paper evaluates the effectiveness of Orbital Torus Imaging (OTI) in recovering the Milky Way's gravitational potential using simulated data, demonstrating high accuracy in most cases despite system evolution.

Contribution

It applies OTI to a realistic cosmological simulation to assess its accuracy and sensitivity, providing validation and error analysis for future survey applications.

Findings

OTI recovers vertical acceleration profiles within 3 sigma errors for 94% of volumes.

OTI's accuracy decreases for large scale heights and low densities at certain heights.

Realistic error bars are derived, aiding interpretation of survey data.

Abstract

Orbital Torus Imaging (OTI) is a dynamical inference method for determining the Milky Way's gravitational potential using stellar survey data. OTI uses gradients in stellar astrophysical quantities, such as element abundances, as functions of dynamical quantities, like orbital actions or energy, to estimate the Galactic mass distribution, assuming axisymmetry and steady-state of the system. While preliminary applications have shown promising outcomes, its sensitivity to disequilibrium effects is unknown. Here, we apply OTI to a benchmark Feedback in Realistic Environments (FIRE-2) cosmological hydrodynamic simulation, m12i, which enables a comparative analysis between known FIRE-2 vertical acceleration profiles and total surface mass densities to the analogous OTI-inferred results. We quantify OTI's accuracy within solar-analog volumes embedded in the simulated galactic disk. Despite a dynamically-evolving system, we find that OTI recovers the known vertical acceleration profiles within 3 sigma/1 sigma errors for 94%/75% of the volumes considered. We discuss the method's sensitivity to the local, instantaneous structure of the disk, reporting a loss in accuracy for volumes that have large (>1.5 kpc) scale heights and low total density at z=1.1 kpc. We present realistic OTI error bars from both MCMC sampling and bootstrapping the FIRE-2 simulated data, which provides a touchstone for interpreting results obtained from current and forthcoming surveys such as SDSS-V, Gaia, WEAVE, and 4MOST.