The Pristine survey XVIII: C-19: Tidal debris of a dark matter-dominated
  globular cluster?
  The recently discovered C-19 stellar stream is a collection of kinematically
associated metal-poor stars in the halo of the Milky Way lacking an obvious
progenitor. The stream spans an arc of ~15 degrees on the sky, and
orbit-fitting suggests an apocentric distance of ~20 kpc and a pericentre of
~10 kpc. The narrow metallicity dispersion of stars with available spectra,
together with light element abundance variations, suggest a globular cluster
(GC) origin. The observed metallicity ([Fe/H] ~ -3.4), however, is much lower
than that of any known GC. In addition, the width and velocity dispersion of
the stream are similar to those expected from disrupting dwarf galaxies, and
substantially larger than the tidal debris of GCs able to disrupt on C-19's
orbit. We propose here an unconventional model where the C-19 progenitor is a
dark matter-dominated stellar system with GC-like abundance patterns. We use
N-body simulations to show that the tidal disruption of a ~100 pc King-model
stellar component embedded in a ~20 km/s cuspy cold dark matter halo yields
debris consistent with C-19's observed width and velocity dispersion. The
stellar component of the progenitor is fully disrupted, and is spread over two
distinct streams; one corresponding to C-19 and another possibly hiding behind
the Galactic plane. If such companion stream were found, it would suggest that
dark matter-dominated dwarfs may also develop GC-like enrichment patterns, a
finding that would inform our theoretical understanding of the formation of
multiple populations in GCs and dwarf galaxies alike.
