Presentation #342.01 in the session “Galaxy Evolution & Populations”.
Galactic disks are continuously subject to influences on their dynamical evolution from multiple sources - including the dark matter halo, satellite systems and their own self-gravity. Even the Milky Way - a relative quiet backwater in the Universe - shows abundant signatures of these ongoing actions and reactions. Disentangling the interlocked causes of these signatures is a challenge to the field. This paper presents an analysis of an N-body simulation of a Milky Way-like disk interacting with a satellite dwarf galaxy with mass and orbit similar to the Sagittarius dwarf galaxy. The aim is to develop a holistic view of how each galactic component in the simulation uniquely contributes to the overall complex dynamical evolution of the disk. Each component’s (R,phi,z) accelerations on the disk plane are represented as a superposition of fourier modes and directly compared over time. Sagittarius’s influence is mostly confined to impact events, serving as impulses to drive the evolution of the other components. The resultant wake in the dark matter halo dominates the outer disk. Most of the major structures present in the disk, such as the spiral arms and the bar, are created by disk self-gravity sustaining the distortions in reaction to Sgr passages. Hence the wave-like features in astrometric surveys such as Gaia DR2 are due all three: the satellite encounters, the wake in the halo and a dynamically active disk. This work demonstrates how basis function expansions are useful tools in the disentanglement of dynamical processes from one component to another to clarify and characterize these complex interactions.