Globular clusters as tracers of the dark matter content ofdwarfs in galaxy clusters

Globular clusters (GCs) are often used to estimate the dark matter content of galaxies, especially dwarfs, where other kinematic tracers are lacking. These estimates typically assume spherical symmetry and dynamical equilibrium, assumptions that may not hold for the sparse GC population of dwarfs in galaxy clusters. We use a catalog of GCs tagged onto the Illustris simulation to study the accuracy of GC-based mass estimates. We focus on galaxies in the stellar mass range 10⁸ − 10^11.8 M_sun identified in 9 simulated Virgo-like clusters. Our results indicate that mass estimates are, on average, quite accurate in systems with GC numbers N_GC ≥ 10 and where the uncertainty of individual GC line-of-sight velocities is smaller than the inferred velocity dispersion, σ_GC . In cases where N_GC ≤ 10, however, biases may result depending on how σ_GC is computed. We provide calibrations that may help alleviate these biases in methods widely used in the literature. As an application, we find a number of dwarfs with M _∗ ∼ 10 ^8.5 M_sun (comparable to the ultradiffuse galaxy DF2, notable for the low σ_GC of its 10 GCs) with σ _GC ∼ 7 - 15 km s ⁻¹ . These DF2 analogs correspond to relatively massive systems at their infall time (M₂₀₀ ∼ 1 - 3 × 10¹¹ M_sun) which have retained only 3-17 GCs and have been stripped of more than 95% of their dark matter. Our results suggest that extreme tidal mass loss in otherwise normal dwarf galaxies may be a possible formation channel for ultradiffuse objects like DF2.