Dark matter halo cores and the tidal survival of Milky Way satellites

TL;DR

This study uses N-body simulations to examine how dark matter core sizes affect the tidal disruption of Milky Way satellites, constraining dark matter models based on satellite survival.

Contribution

It provides new constraints on dark matter core sizes by linking satellite survival to core size, challenging certain self-interacting dark matter models.

Findings

Satellites with cores larger than 1% of their initial NFW scale radius cannot survive Hubble time on close orbits.

Ultra-faint satellites like Tucana 3 require core sizes smaller than ~2 pc to survive multiple orbits.

Many satellites likely have negligible core sizes, consistent with CDM cusps.

Abstract

The cuspy central density profiles of cold dark matter (CDM) haloes make them highly resilient to disruption by tides. Self-interactions between dark matter particles, or the cycling of baryons, may result in the formation of a constant-density core which would make haloes more susceptible to tidal disruption. We use N-body simulations to study the evolution of NFW-like "cored" subhaloes in the tidal field of a massive host, and identify the criteria and timescales for full tidal disruption. Our results imply that the survival of Milky Way satellites places constraints on the sizes of dark matter cores. Indeed, we find that no subhaloes with cores larger than 1 per cent of their initial NFW scale radius can survive for a Hubble time on orbits with pericentres <10 kpc. A satellite like Tucana 3, with pericentre ~3.5 kpc, must have a core size smaller than ~2 pc to survive just three orbital periods on its current orbit. The core sizes expected in self-interacting dark matter (SIDM) models with a velocity-independent cross section of 1 cm^2/g seem incompatible with ultra-faint satellites with small pericentric radii, such as Tuc 3, Seg 1, Seg 2, Ret 2, Tri 2, and Wil 1, as these should have fully disrupted if accreted on to the Milky Way >10 Gyr ago. These results suggest that many satellites have vanishingly small core sizes, consistent with CDM cusps. The discovery of further Milky Way satellites on orbits with small pericentric radii would strengthen these conclusions and allow for stricter upper limits on the core sizes.