Signatures of minor mergers in Milky Way-like disc kinematics: Ringing revisited

TL;DR

This study uses N-body simulations to analyze how minor mergers induce observable 'ringing' features in the Milky Way's disc, revealing insights into the merger history through stellar kinematics.

Contribution

It demonstrates that phase-space structures from minor mergers can be detected in energy-angular momentum space, improving observational prospects and understanding of galactic evolution.

Findings

Clumps in velocity space become closer over time, indicating the impact epoch.

Azimuthal dependence affects phase-space structures, linked to the perturber's trajectory.

Energy-angular momentum space reveals merger signatures more clearly than velocity space.

Abstract

By means of N-body simulations we study the response of a galactic disc to a minor merger event. We find that non-self-gravitating, spiral-like features are induced in the thick disc. As we have shown in a previous work, this "ringing" also leaves an imprint in velocity space (the u-v plane) in small spatial regions, such as the solar neighbourhood. As the disc relaxes after the event, clumps in the u-v plane get closer with time, allowing us to estimate the time of impact. In addition to confirming the possibility of this diagnostic, here we show that in a more realistic scenario, the in-fall trajectory of the perturber gives rise to an azimuthal dependence of the structure in phase-space. We also find that the space defined by the energy and angular momentum of stars is a better choice than velocity space, as clumps remain visible even in large local volumes. This makes their observational detection much easier since one need not be restricted to a small spatial volume. We show that information about the time of impact, the mass of the perturber, and its trajectory is stored in the kinematics of disc stars.