Tying Dark Matter to Baryons with Self-interactions
  Self-interacting dark matter (SIDM) models have been proposed to solve the
small-scale issues with the collisionless cold dark matter (CDM) paradigm. We
derive equilibrium solutions in these SIDM models for the dark matter halo
density profile including the gravitational potential of both baryons and dark
matter. Self-interactions drive dark matter to be isothermal and this ties the
core sizes and shapes of dark matter halos to the spatial distribution of the
stars, a radical departure from previous expectations and from CDM predictions.
Compared to predictions of SIDM-only simulations, the core sizes are smaller
and the core densities are higher, with the largest effects in baryon-dominated
galaxies. As an example, we find a core size around 0.5 kpc for dark matter in
the Milky Way, more than an order of magnitude smaller than the core size from
SIDM-only simulations, which has important implications for indirect searches
of SIDM candidates.
