The Once and Future Andromeda Stream

TL;DR

This study uses high-resolution simulations to analyze the interaction between an accreting satellite and M31, revealing the formation of the Stream, shells, and diffuse arcs, and constraining the satellite's mass based on the galaxy's current structure.

Contribution

First to show the self-gravitating response of M31's components to a satellite using high-res N-body simulations, reproducing observed features and constraining satellite mass.

Findings

Reproduced the Stream and shells around M31.

Identified diffuse arcs as remnants of earlier collisions.

Constrained satellite mass to be less than or equal to 5×10^9 solar masses.

Abstract

The interaction between an accreting satellite and the Andromeda galaxy (M31) has been studied analytically and numerically, using a high-resolution N-body simulation with $4\times10^7$ particles. For the first time, we show the self-gravitating response of the disk, the bulge, and the dark matter halo of M31 to an accreting satellite. We reproduce the Stream and the shells at the East and West side of M31, by following the evolution of the collision 4 Gyr into the future, and show that recently discovered diffuse arcs on the south side of the minor axis are the remnants of a similar collision that occurred 3-4 Gyr earlier than the Stream event. The present day integrity of the M31 disk constrains the satellite mass to be $M \leq 5\times10^9 M_\odot$. The stars that were originally in the center of the satellite are now in the east shell. Therefore, observations in this region might reveal additional clues about the nature of satellite, such as the central core and any metallicity gradient.