New data from the $\textit{ Gaia}$ satellite, when combined with accurate photometry from the Pan-STARRS survey, allow us to accurately estimate the properties of the GD-1 stream. Here, we analyze the stellar density perturbations in the GD-1 stream and show that they cannot be due to known baryonic structures like giant molecular clouds, globular clusters, or the Milky Way's bar or spiral arms. A joint analysis of the GD-1 and Pal 5 streams instead requires a population of dark substructures with masses $\approx 10^{ 7}$ to $10^9 \ M_{ \rm{ \odot}}$. We infer a total abundance of dark subhalos normalised to standard cold dark matter $n_{ \rm sub}/n_{ \rm sub, CDM} = 0.4 ^{ +0.3}_{ -0.2}$ ($68 \%$), which corresponds to a mass fraction contained in the subhalos $f_{ \rm{ sub}} = 0.14 ^{ +0.11}_{ -0.07} \%$, compatible with the predictions of hydrodynamical simulation of cold dark matter with baryons.
Categories: astro-ph.GA astro-ph.CO