On the Stability of Satellite Planes I: Effects of Mass, Velocity, Halo Shape and Alignment

TL;DR

This study investigates the stability of satellite galaxy planes around galaxies like Andromeda, revealing their fragility and dependence on halo shape, which challenges current cosmological models of their long-term existence.

Contribution

It provides the first detailed analysis of how dark matter halo shape and orbital orientation affect the survivability of satellite planes.

Findings

Planes are fragile and sensitive to halo shape.

Long-lived planes only exist in spherical halos with polar orbits.

The observed Andromeda plane's tilt suggests it is a transient feature.

Abstract

The recently discovered vast thin plane of dwarf satellites orbiting the Andromeda Galaxy (M31) adds to the mystery of the small scale distribution of the Local Group's galaxy population. Such well defined planar structures are apparently rare occurrences in cold dark matter cosmological simulations, and we lack a coherent explanation of their formation and existence. In this paper, we explore the long-term survivability of thin planes of dwarfs in galactic halos, focusing, in particular, on systems mimicking the observed Andromeda distribution. The key results show that, in general, planes of dwarf galaxies are fragile, sensitive to the shape of the dark matter halo and other perturbing effects. In fact, long lived planes of satellites only exist in polar orbits in spherical dark matter halos, presenting a challenge to the observed Andromeda plane which is significantly tilted with respect to the optical disk. Our conclusion is that, in standard cosmological models, planes of satellites are generally short lived, and hence we must be located at a relatively special time in the evolution of the Andromeda Plane, lucky enough to see its coherent pattern.