Effect of the Large Magellanic Cloud on the kinematics of Milky Way satellites and virial mass estimate

TL;DR

This study investigates how the passage of a Large Magellanic Cloud affects the kinematics of Milky Way satellites and introduces a new mass estimator that accounts for these effects, leading to a refined Milky Way mass estimate.

Contribution

It presents a new halo mass estimator based on satellite velocities and distances, calibrated with simulations, and demonstrates its effectiveness during LMC-like passages.

Findings

Velocity distribution develops a high-velocity tail during LMC passage.

Correcting for LMC effects aligns satellite velocities with lower halo mass models.

New mass estimator has 8% scatter and accurately estimates the Milky Way's virial mass.

Abstract

We present a study illustrating the effects of the passage of a Large Magellanic Cloud (LMC) mass satellite on the distance and velocity distributions of satellites in $\Lambda+$Cold Dark Matter simulations of Milky Way (MW) sized halos. In agreement with previous studies, we find that during such a passage the velocity distribution develops a high-velocity tail, which can bias velocity-based virial halo mass estimates. When the velocity distribution of MW satellites is corrected for effects of the LMC passage, it is consistent with the distributions in halos of masses as low as $M_{\rm 200c}=8\times 10^{11}\, M_\odot$ and as high as $1.5\times 10^{12}\,M_\odot$. We present a new halo mass estimator $M_{\rm 200c}=c\sigma^2_{\rm 3D}r_{\rm med}$, where $c$ is the coefficient calibrated using satellite systems in the simulated MW-sized halos, $\sigma^2_{\rm 3D}$ is the variance of 3D velocities taken with the sign of the radial velocity of each satellite, and $r_{\rm med}$ is the median halocentric distance of the satellites. We show that the estimator has only $s=8\%$ scatter around the median relation of the estimated and true halo masses and deviates by $<2s$ from the median during the pericentric passage of an LMC-like subhalo. This is because $\sigma^2_{\rm 3D}$ and $r_{\rm med}$ deviate in the opposite directions during such passages. We apply the estimator to the MW satellite system and estimate the virial mass of the Milky Way of $M_{\rm 200c}=9.96\pm 1.45\times 10^{11}\, M_\odot$, in good agreement with several recent estimates using other methods.