The orbital poles of Milky Way satellite galaxies: a rotationally supported disc-of-satellites

TL;DR

This study compares the orbital poles of Milky Way satellite galaxies with CDM simulations, revealing that MW satellites form a rotationally supported disc, unlike the random distribution in simulations, suggesting a tidal origin.

Contribution

It demonstrates that MW satellite orbital poles form a disc supported by rotation, contrasting with the randomness in CDM simulations, implying a different origin for MW satellites.

Findings

MW satellite orbital poles form a rotationally supported disc

CDM simulations show random orbital and spatial distributions

Most MW satellites likely have a tidal origin rather than being DM sub-structures

Abstract

Available proper motion measurements of Milky Way (MW) satellite galaxies are used to calculate their orbital poles and projected uncertainties. These are compared to a set of recent cold dark-matter (CDM) simulations, tailored specifically to solve the MW satellite problem. We show that the CDM satellite orbital poles are fully consistent with being drawn from a random distribution, while the MW satellite orbital poles indicate that the disc-of-satellites of the Milky Way is rotationally supported. Furthermore, the bootstrapping analysis of the spatial distribution of theoretical CDM satellites also shows that they are consistent with being randomly drawn. The theoretical CDM satellite population thus shows a significantly different orbital and spatial distribution than the MW satellites, most probably indicating that the majority of the latter are of tidal origin rather than being DM dominated sub-structures. A statistic is presented that can be used to test a possible correlation of satellite galaxy orbits with their spatial distribution.