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