An enigmatic population of luminous globular clusters in a galaxy lacking dark matter

TL;DR

This study analyzes luminous globular clusters in a dark matter-deficient galaxy, revealing their properties and challenging the universality of globular cluster luminosity functions, suggesting dark matter is not essential for their formation.

Contribution

It demonstrates that metal-poor globular clusters can form without dark matter halos, contrasting with previous assumptions about galaxy formation.

Findings

Globular clusters have an average size of 6.2 pc and ellipticity of 0.18.

Clusters are older than 9 Gyr with metallicity [Fe/H] = -1.35.

The galaxy's globular cluster system deviates from known mass relations.

Abstract

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.