Luminous globular clusters in NGC 5128

An exciting confirmation of this model is the detection of overmassive black holes in the centers of some UCDs, which also lead to elevated dynamical mass-to-light ratios (M/Ldyn). Here we present new high-resolution spectroscopic observations of 321 luminous GC candidates in the massive galaxy NGC 5128/Centaurus A. Using these data we confirm 27 new luminous GCs, and measure velocity dispersions for 57 luminous GCs (with g-band luminosities between 2.5x10^5^ and 2.5x10^7^L_{sun}_), of which 48 are new measurements.

Combining these data with size measurements from Gaia, we determine the M/L_dyn_ for all 57 luminous GCs. We see a clear bimodality in the M/L_dyn_ distribution, with a population of normal GCs with mean M/L_dyn_=1.51+/-0.31, and a second population of ~20 GCs with elevated mean M/L_dyn_=2.68+/-0.22. We show that black holes with masses ~4%-18% of the luminous GCs can explain the elevated mass-to-light ratios.