The haloes of bright satellite galaxies in a warm dark matter universe

TL;DR

This paper demonstrates that warm dark matter models resolve the discrepancy between observed satellite galaxy kinematics and cold dark matter simulations by producing less concentrated haloes with more realistic velocities.

Contribution

It shows that warm dark matter haloes naturally align with observed satellite galaxy velocities, addressing issues found in cold dark matter models.

Findings

Warm dark matter haloes are less concentrated than cold dark matter haloes.

Satellite galaxy velocities in warm dark matter models match observations.

Cold dark matter simulations predict too many overly concentrated subhaloes.

Abstract

High resolution N-body simulations of galactic cold dark matter haloes indicate that we should expect to find a few satellite galaxies around the Milky Way whose haloes have a maximum circular velocity in excess of 40 kms. Yet, with the exception of the Magellanic Clouds and the Sagittarius dwarf, which likely reside in subhaloes with significantly larger velocities than this, the bright satellites of the Milky Way all appear to reside in subhaloes with maximum circular velocities below 40 kms. As recently highlighted by Boylan-Kolchin et al., this discrepancy implies that the majority of the most massive subhaloes within a cold dark matter galactic halo are much too concentrated to be consistent with the kinematic data for the bright Milky Way satellites. Here we show that no such discrepancy exists if haloes are made of warm, rather than cold dark matter because these haloes are less concentrated on account of their typically later formation epochs. Warm dark matter is one of several possible explanations for the observed kinematics of the satellites.