On Asymmetric Distributions of Satellite Galaxies

TL;DR

This paper investigates the causes of asymmetric satellite galaxy distributions, concluding that associations falling into larger halos can produce observed asymmetries, with survival times depending on the gravitational potential.

Contribution

It introduces an analytical model for the dispersal time of satellite associations and explains how such groups can create asymmetric satellite distributions.

Findings

Asymmetric satellite distributions cannot be caused by tidal effects from the Milky Way.

Associations of satellites can survive longer in logarithmic potentials than in Keplerian ones.

A group of about 10 dwarfs falling into M31 could produce the observed asymmetry.

Abstract

We demonstrate that the asymmetric distribution of M31 satellites cannot be produced by tides from the Milky Way as such effects are too weak. However, loosely bound associations and groups of satellites can fall into larger haloes and give rise to asymmetries. We compute the survival times for such associations. We prove that the survival time is always shortest in Keplerian potentials, and can be ~ 3 times longer in logarithmic potentials. We provide an analytical formula for the dispersal time in terms of the size and velocity dispersion of the infalling structure. We show that, if an association of ~10 dwarfs fell into the M31 halo, its present aspect would be that of an asymmetric disk of satellites. We also discuss the case of cold substructure in the Andromeda II and Ursa Minor dwarfs.