NGC 5128's Globular Cluster System: Is There a Dark Side?

Abstract

Dynamical mass estimates (${\cal M}_{\rm dyn}$) and mass-to-light ratios ($\Upsilon_{\rm dyn}$) were derived for a sample of NGC 5128's globular clusters (GCs). We find two distinct sequences in the $\Upsilon_{\rm dyn}$ − ${\cal M}_{\rm dyn}$ plane, which are well fit by power laws of the forms $\Upsilon_{\rm dyn}\propto {\cal M}_{\rm dyn}^{0.33\pm0.04}$ and $\Upsilon_{\rm dyn}\propto {\cal M}_{\rm dyn}^{0.91\pm0.04}$. The former traces bright “classical” GCs, and the latter represents objects that are dynamically dominated by large dark matter components or by abnormally massive central black holes.