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 ≳65 M⊙​ 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 ∼5,000 times denser than predicted by simulation to be
constrained by the wide binary catalogue.Comment: 21 pages, 23 figure