Program: GN-2014A-Q-4

We propose to observe three of the most massive UCDs with Gemini/NIFS to resolve their kinematics. Massive UCDs above 10 million solar masses are observed to have M/L ratios significantly higher than stellar population model predictions. The cause of these high M/L ratios is not yet known. They can be explained by the presence of massive BHs with masses of order 10% of the stellar component. These overmassive black holes would be expected if UCDs are tidally stripped galaxy nuclei representing ~1% of the mass of their progenitor galaxy. On the other hand, the elevated M/L ratios could also be explained if their stars have a non-standard Initial Mass Function (IMF). Dynamical modeling of the proposed observations will be able to distinguish between these possibilities by simultaneously determining the stellar M/L and constraining the BH mass. We will detect BHs with masses more than a few percent of the UCD stellar mass. Detection of a BH in even one of the objects would be important, because it would suggest the presence of a large population of previously unknown BHs. Alternatively, non-detections of BHs would provide evidence for non-standard IMFs in UCDs.