Dynamics of Stellar Disk Tilting from Satellite Mergers

TL;DR

This study uses N-body simulations to understand how satellite galaxy mergers can cause the Milky Way's stellar disk to tilt, with implications for dark matter detection and galactic history.

Contribution

It provides a first-principles model of disk tilting dynamics and shows that recent mergers like Gaia-Sausage-Enceladus can significantly tilt the galactic disk.

Findings

Disk tilting can be substantial during cosmological mergers.

The Milky Way's disk may still be tilting due to past mergers.

Disk tilting affects local dark matter distribution and detection experiments.

Abstract

The Milky Way's stellar disk can tilt in response to torques that result from infalling satellite galaxies and their associated tidal debris. In this work, we explore the dynamics of disk tilting by running N-body simulations of mergers in an isolated, isotropic Milky Way-like host galaxy, varying over satellite virial mass, initial position, and orbit. We develop and validate a first-principles understanding of the dynamics that govern how the host galaxy's stellar disk responds to the satellite's dark matter debris. We find that the degree of disk tilting can be large for cosmologically-motivated merger histories. In particular, our results suggest that the Galactic disk may still be tilting in response to Gaia-Sausage-Enceladus, one of the most significant recent mergers in the Milky Way's history. These findings have implications for terrestrial direct detection experiments as disk tilting changes the relative location of the Sun with respect to dark matter substructure left behind by a merging galaxy.