1705.08513
Extensive globular cluster systems associated with ultra diffuse galaxies in the Coma cluster
van Dokkum, et al
Present HST imaging of 2 UDGs with measured stellar velocity dispersions in the Coma cluster. The galaxies, Dragonfly 44 and DFX1, have effective radii of 4.7 kpc and 3.5 kpc and velocity dispersions of 47±8 km/s and 30±7 km/s, respectively. Both galaxies are associated with a striking number of compact objects, tentatively identified as globular clusters: N_gc=74±18 for Dragonfly 44 and N_gc = 62±17 for DFX1. The number of globular clusters is far higher than expected from the luminosities of the galaxies but is consistent with expectations from the empirical relation between dynamical mass and globular cluster count defined by other galaxies. Combining the data for these 2 objects with previous HST observations of Coma UDGs, find that most have large globular cluster populations for their luminosities, in contrast to a recent study of a similar sample by Amorisco+2017, but consistent with earlier results for individual galaxies. The Harris+2017 relation between globular cluster count and DM halo mass implies a median halo mass of M_halo~1.5e11 Msun for the 16 Com UDGs that have been observed with HST so far, with the largest and brightest having M_halo~5e11 Msun.
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