C-19 and Hot, Wide Star Streams

The C-19 star stream has the abundance characteristics of an unusually metal-poor globular cluster but kinematically is uncharacteristically hot and wide for a cluster stream, having a line-of-sight velocity dispersion of 7 ± 2 km s−1 and a 1σ width of 240 pc. We show that the tidal dissolution of an old, lower-mass globular cluster in a cold dark matter (CDM) galactic halo can create a hot, wide stream currently near orbital apocenter. A cosmological Milky Way n-body simulation motivates the parameters for an evolving Milky Way halo potential containing an orbiting subhalo population in which we model a star cluster progenitor of C-19. The same model parameters have been used for a GD-1 stream model. The ∼7 km s−1 velocity dispersion is readily accomplished with an evolving CDM subhalo population, a progenitor cluster mass ≃2 × 104M⊙, and an orbit that keeps the progenitor orbital pericenter within about 10 kpc of the Milky Way dark halo or its precursors.