Exploring the Sgr-Milky-Way-disc interaction using high resolution N-body simulations

TL;DR

This study uses high-resolution N-body simulations to investigate the impact of the Sagittarius dwarf galaxy's merger with the Milky Way on the Galactic disc, finding that Sgr alone cannot explain observed vertical perturbations.

Contribution

The paper presents a comprehensive set of high-resolution N-body simulations modeling Sgr-Milky Way interactions, assessing their effects on disc dynamics and comparing results with Gaia data.

Findings

Simulations do not fully match Gaia observations of vertical perturbations.

Most similar simulation's Sgr mass exceeds observed values.

Simulated asymmetry features differ from observed structures.

Abstract

The ongoing merger of the Sagittarius (Sgr) dwarf galaxy with the Milky Way is believed to strongly affect the dynamics of the Milky Way's disc. We present a suite of 13 $N$-body simulations, with 500 million to 1 billion particles, modelling the interaction between the Sagittarius dwarf galaxy (Sgr) and the Galactic disc. To quantify the perturbation to the disc's structure and dynamics in the simulation, we compute the number count asymmetry and the mean vertical velocity in a solar-neighbourhood-like volume. We find that overall the trends in the simulations match those seen in a simple one-dimensional model of the interaction. We explore the effects of changing the mass model of Sgr, the orbital kinematics of Sgr, and the mass of the Milky Way halo. We find that none of the simulations match the observations of the vertical perturbation using Gaia Data Release 2. In the simulation which is the most similar, we find that the final mass of Sgr far exceeds the observed mass of the Sgr remnant, the asymmetry wavelength is too large, and the shape of the asymmetry doesn't match past $z \approx 0.7$ kpc. We therefore conclude that our simulations support the conclusion that Sgr alone could not have caused the observed perturbation to the solar neighbourhood.