Probing the nature of dark matter with accreted globular cluster streams
  The steepness of the central density profiles of dark matter (DM) in low-mass
galaxy halos (e.g. dwarf galaxies) is a powerful probe of the nature of DM. We
propose a novel scheme to probe the inner profiles of galaxy subhalos using
stellar streams. We show that the present day morphological and dynamical
properties of accreted globular cluster (GC) streams - those produced from
tidal stripping of GCs that initially evolved within satellite galaxies and
later merged with the Milky Way (MW) - are sensitive to the central DM density
profile and mass of their parent satellites. GCs that accrete within cuspy CDM
subhalos produce streams that are physically wider and dynamically hotter than
streams that accrete inside cored subhalos. A first comparison of MW streams
"GD-1" and "Jhelum" (likely of accreted GC origin) with our simulations
indicates a preference for cored subhalos. If these results hold up in future
data, the implication is that either the DM cusps were erased by baryonic
feedback, or their subhalos naturally possessed cored density profiles implying
DM models beyond CDM. Moreover, accreted GC streams are highly structured and
exhibit complex morphological features (e.g., parallel structures and "spurs").
This implies that the accretion scenario can naturally explain the recently
observed peculiarities in some of the MW streams. We also propose a novel
mechanism for forming "gaps" in streams when the remnant of the parent subhalo
later passes through the stream. This encounter can last a longer time (and
have more of an impact) than the random encounters with DM subhalos previously
considered, because the GC stream and its parent subhalo are on similar orbits
with small relative velocities. Current and future surveys of the MW halo will
uncover numerous faint stellar streams and provide the data needed to
substantiate our preliminary tests with this new probe of DM.
