Implications for galaxy formation models from observations of globular clusters around ultradiffuse galaxies

We present an analysis of Hubble Space Telescope observations of globular clusters (GCs) in six ultradiffuse galaxies (UDGs) in the Coma cluster, a sample that represents UDGs with large effective radii (R-e), and use the results to evaluate competing formation models. We eliminate two significant sources of systematic uncertainty in the determination of the number of GCs, N-GC by using sufficiently deep observations that (i) reach the turnover of the globular cluster luminosity function (GCLF) and (ii) provide a sufficient number of GCs with which to measure the GC number radial distribution. We find that N-GC for these galaxies is on average similar to 20, which implies an average total mass, M-total, similar to 10(11) M-circle dot when applying the relation between N-GC and M-total. This value of N-GC lies at the upper end of the range observed for dwarf galaxies of the same stellar mass and is roughly a factor of two larger than the mean. The GCLF, radial profile, and average colour are more consistent with those observed for dwarf galaxies than with those observed for the more massive (L*) galaxies, while both the radial and azimuthal GC distributions closely follow those of the stars in the host galaxy. Finally, we discuss why our observations, specifically the GC number and GC distribution around these six UDGs, pose challenges for several of the currently favoured UDG formation models.

Automated summary

This study analyses the observations of globular clusters in six ultradiffuse galaxies and evaluates competing formation models. The results suggest that the globular cluster number and distribution in these galaxies are more consistent with dwarf galaxies rather than more massive galaxies.