Constraining Dark Matter Substructure With Gaia Wide Binaries

TL;DR

This study uses Gaia wide binary data to place constraints on dark matter substructure, showing that certain subhalo masses and densities cannot constitute all of the Milky Way's dark matter without disrupting observed binaries.

Contribution

It introduces a method to constrain dark matter subhalos using wide binary distributions, independent of their formation mechanisms.

Findings

Subhalos with masses > 65 M_sun are constrained from making up all dark matter.

Constraints depend on subhalo size and density profile, with denser profiles being more constrained.

Cold dark matter subhalos must be over 5,000 times denser than simulations to be consistent with observations.

Abstract

We use a catalogue of stellar binaries with wide separations (up to 1 pc) identified by the Gaia satellite to constrain the presence of extended substructure within the Milky Way galaxy. Heating of the binaries through repeated encounters with substructure results in a characteristic distribution of binary separations, allowing constraints to be placed independent of the formation mechanism of wide binaries. Across a wide range of subhalo density profiles, we show that subhalos with masses $\gtrsim 65 \ M_\odot$ and characteristic length scales similar to the separation of these wide binaries cannot make up 100% of the Galaxy's dark matter. Constraints weaken for subhalos with larger length scales and are dependent on their density profiles. For such large subhalos, higher central densities lead to stronger constraints. Subhalos with density profiles similar to those expected from cold dark matter must be at least $\sim 5,000$ times denser than predicted by simulation to be constrained by the wide binary catalogue.