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

Abstract

By means ofN-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 (theu-vplane) in small spatial regions, such as the solar neighbourhood. As the disc relaxes after the event, clumps in theu-vplane 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 infall 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. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.