A Holistic Review of a Galactic Interaction

TL;DR

This study uses N-body simulations to analyze how the Sagittarius dwarf galaxy influences the Milky Way's disc, dark matter halo, and overall structure during a minor merger, revealing the roles of each component in disc heating and asymmetry formation.

Contribution

It provides a detailed decomposition of the different influences on the galactic disc during a minor merger, highlighting the roles of the satellite, dark matter halo, and self-gravity in disc evolution.

Findings

Satellite effects are localized around disc passages.

Dark matter halo distortion amplifies satellite influence.

Disc asymmetries and bar formation result from these interactions.

Abstract

Our situation as occupants of the Milky Way (MW) Galaxy, bombarded by the Sagittarius dwarf galaxy, provides an intimate view of physical processes that can lead to the dynamical heating of a galactic disc. While this evolution is instigated by Sagittarius, it is also driven by the intertwined influences of the dark matter halo and the disc itself. We analyse an N-body simulation following a Sagittarius-like galaxy interacting with a MW-like host to disentangle these different influences during the stages of a minor merger. The accelerations in the disc plane from each component are calculated for each snapshot in the simulation, and then decomposed into Fourier series on annuli. The analysis maps quantify and compare the scales of the individual contributions over space and through time: (i) accelerations due to the satellite are only important around disc passages; (ii) the influence around these passages is enhanced and extended by the distortion of the dark matter halo; (iii) the interaction drives disc asymmetries within and perpendicular to the plane and the self-gravity of these distortions increase in importance with time eventually leading to the formation of a bar. These results have interesting implications for identifying different influences within our own Galaxy. Currently, Sagittarius is close enough to a plane crossing to search for localized signatures of its effect at intermediate radii, the distortion of the MW's dark matter halo should leave its imprint in the outer disc and the disc's own self-consistent response is sculpting the intermediate and inner disc.