The Dynamics of Satellite Galaxy Planes

Abstract

First created to explain the discrepancies between the predictions and observations, dark matter makes up around 25% of the universe’s energy budget. Λ Cold Dark Matter (ΛCDM) cosmology accurately represents the large scale structure of the current universe, but shows significant variation in the small ℨscale structure. The recently discovered planes of dwarf satellite galaxies orbiting the Milky Way and M31 adds to the mystery of the small scale distribution of the Local Group. Though similar planar structures are seemingly rare occurrences in ΛCDM cosmological simulations, they could shed light on the dark matter environment of their host galaxies. This thesis explores the factors that affect the stability and longevity of a plane of satellite galaxies in a M31-like system, with numerical simulations. The most influential factors are the shape of the host dark matter distribution, and the plane’s inclination to the axes of the dark halo. For the M31 plane to be older than 4 Gyrs, it either needs to exist in a near spherical dark halo, or be aligned with the dark halo axes. Lifetimes of planar formations inclined to the halo axes, in a prolate/ oblate halo are limited to ≤3 Gyrs, and a populous environment of dark subhalos disperse the planar formation by increasing its thickness over 3 Gyrs. As the fraction of total dark matter mass that is included in the subhalo population reaches ∼40%, the overall shape of the dark matter distribution also becomes unstable over ≥5 Gyrs. Massive, non-planar, interloping galaxies have a notable effect on planes only when their mass is ≥ 1010 M, and any orbital plane misalignments exaggerate this effect. The shape of the M31 host halo also exerts a significant influence on the orbit of M33. In conclusion, planes of satellites are generally short lived in ΛCDM cosmology, and hence we must be located at a special time in the evolution of the M31 plane, and are lucky enough to see its coherent pattern