An enigmatic population of luminous globular clusters in a galaxy
  lacking dark matter
  We recently found an ultra diffuse galaxy (UDG) with a half-light radius of
R_e = 2.2 kpc and little or no dark matter. The total mass of NGC1052-DF2 was
measured from the radial velocities of bright compact objects that are
associated with the galaxy. Here we analyze these objects using a combination
of HST imaging and Keck spectroscopy. Their average size is <r_h> = 6.2+-0.5 pc
and their average ellipticity is <{\epsilon}> = 0.18+-0.02. From a stacked Keck
spectrum we derive an age >9 Gyr and a metallicity of [Fe/H] = -1.35+-0.12.
Their properties are similar to {\omega} Centauri, the brightest and largest
globular cluster in the Milky Way, and our results demonstrate that the
luminosity function of metal-poor globular clusters is not universal. The
fraction of the total stellar mass that is in the globular cluster system is
similar to that in other UDGs, and consistent with "failed galaxy" scenarios
where star formation terminated shortly after the clusters were formed.
However, the galaxy is a factor of ~1000 removed from the relation between
globular cluster mass and total galaxy mass that has been found for other
galaxies, including other UDGs. We infer that a dark matter halo is not a
prerequisite for the formation of metal-poor globular cluster-like objects in
high redshift galaxies.
