Advancing Stellar Streams as a Dark Matter Probe -- I: Evolution of the CDM subhalo population

Abstract: Stellar streams, long thin streams of stars, have been used as sensitive probes of dark matter substructure for over two decades. Gravitational interactions between dark matter substructures and streams lead to the formation of low density "gaps" in streams, with any given stream typically containing no more than a few such gaps. Prior models for the statistics of such gaps have relied on several simplifying assumptions for the properties of the subhalo population in the cold dark matter scenario. With the expected forthcoming increase in the number of streams, and gaps, observed, in this work we develop a more detailed model for the statistics of subhalos interacting with streams, and test some of the assumptions made in prior works. Instead of using simple fits to N-body estimates of subhalo population statistics at z = 0 as in previous work, we make use of realizations of time-dependent subhalo populations generated from a fully physical model, incorporating structure formation, and subhalo orbital evolution, including tidal heating and stripping physics, which has been carefully calibrated to match results of cosmological N-body simulations. We find that this model predicts up to 60% more gaps on average in Pal-5-like streams than prior works.