Monochromatic Globular Clusters as a Critical Test of Formation Models for the Dark Matter–deficient Galaxies NGC 1052-DF2 and NGC 1052-DF4

Abstract It was recently proposed that the dark matter–deficient ultradiffuse galaxies DF2 and DF4 in NGC 1052 group could be products of a “bullet dwarf” collision between two gas-rich progenitor galaxies. In this model, formed at same time immediate aftermath collision, strong prediction is their globular clusters should have nearly identical stellar populations. Here we test by measuring accurate V 606 − I 814 colors from deep HST/ACS imaging. We find are extremely homogeneous. The mean color difference Δ DF2−DF4 = −0.003 ± 0.005 mag, observed scatter for combined sample 18 with M < −8.6 both σ obs 0.015 0.002 mag. After accounting observational uncertainties stochastic cluster-to-cluster variation number red giants, remaining σ intr = 0.008 − 0.006 + 0.005 Both an order magnitude smaller than other dwarf galaxies, infer bullet scenario passes important falsified it. No formation models predicted extreme uniformity themselves slightly redder clusters, consistent previously measured metallicity difference. Numerical simulations shown such differences expected scenario, as continued to self-enrich after clusters.