Resolving local and global kinematic signatures of satellite mergers with billion particle simulations

TL;DR

This study uses billion-particle simulations to analyze the local and global kinematic signatures of satellite mergers, revealing detailed structures like phase spirals and moving groups in the Milky Way.

Contribution

The paper introduces high-resolution simulations that improve understanding of kinematic features resulting from satellite mergers, linking local structures to global disc asymmetries.

Findings

Local phase spirals are connected to disc asymmetries.

Hercules-like groups migrate outward, matching observed metallicity trends.

Simulations reproduce observed kinematic features without a galactic bar.

Abstract

In this work we present two new $\sim10^9$ particle self-consistent simulations of the merger of a Sagittarius-like dwarf galaxy with a Milky Way-like disc galaxy. One model is a violent merger creating a thick disc, and a Gaia-Enceladus/Sausage like remnant. The other is a highly stable disc which we use to illustrate how the improved phase space resolution allows us to better examine the formation and evolution of structures that have been observed in small, local volumes in the Milky Way, such as the $z-v_z$ phase spiral and clustering in the $v_{\mathrm{R}}-v_{\phi}$ plane when compared to previous works. The local $z-v_z$ phase spirals are clearly linked to the global asymmetry across the disc: we find both 2-armed and 1-armed phase spirals, which are related to breathing and bending behaviors respectively. Hercules-like moving groups are common, clustered in $v_{\mathrm{R}}-v_{\phi}$ in local data samples in the simulation. These groups migrate outwards from the inner galaxy, matching observed metallicity trends even in the absence of a galactic bar. We currently release the best fitting `present day' merger snapshots along with the unperturbed galaxies for comparison.