Kavli Affiliate: David N. Spergel
| First 5 Authors: Jacob Nibauer, Ana Bonaca, David N. Spergel, Adrian M. Price-Whelan, Jenny E. Greene
| Summary:
Stellar streams retain a memory of their gravitational interactions with
small-scale perturbations. While perturbative models for streams have been
formulated in action-angle coordinates, a direct transformation to these
coordinates is only available for static and typically axisymmetric models for
the galaxy. The real Milky Way potential is in a state of disequilibrium,
complicating the application of perturbative methods around an equilibrium
system. Here, we utilize a combination of differentiable simulations and
Hamiltonian perturbation theory to model the leading-order effect of dark
matter subhalos on stream observables. To obtain a perturbative description of
streams, we develop a direct and efficient forward mode differentiation of
Hamilton’s equations of motion. Our model operates in observable coordinates,
allowing us to treat the effects of arbitrary subhalo potentials on streams
perturbatively, while simultaneously capturing non-linear effects due to other
substructures like the infalling LMC or the rotating bar. The model predicts
the velocity dispersion of streams as a function of subhalo statistics,
allowing us to constrain the low-mass range of subhalos down to $sim
10^5~M_odot$. We forecast the velocity dispersion of the GD-1 stream, and find
that observations are in agreement with a CDM subhalo population, with a slight
preference for more dense subhalos. The method provides a new approach to
characterize streams in the presence of substructure, with significantly more
modeling flexibility compared to previous works.
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