How the Self-Interacting Dark Matter Model Explains the Diverse Galactic
  Rotation Curves
  The rotation curves of spiral galaxies exhibit a diversity that has been
difficult to understand in the cold dark matter (CDM) paradigm. We show that
the self-interacting dark matter (SIDM) model provides excellent fits to the
rotation curves of a sample of galaxies with asymptotic velocities in the 25 to
300 km/s range that exemplify the full range of diversity. We only assume the
halo concentration-mass relation predicted by the CDM model and a fixed value
of the self-interaction cross section.In dark matter dominated galaxies,
thermalization due to self-interactions creates large cores and reduces dark
matter densities. In contrast, thermalization leads to denser and smaller cores
in more luminous galaxies, and naturally explains the flat rotation curves of
the highly luminous galaxies. Our results demonstrate that the impact of the
baryons on the SIDM halo profile and the scatter from the assembly history of
halos as encoded in the concentration-mass relation can explain the diverse
rotation curves of spiral galaxies.
