NOAO >   Observing Info >   Approved Programs >   2014A-0241

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Proposal Information for 2014A-0241


PI: Anil Seth, University of Utah, aseth@astro.utah.edu
Address: USA

CoI: Lee Spitler, Macquarie University
CoI: Steffen Mieske, ESO Chile
CoI: Jay Strader, Michigan State University
CoI: Holger Baumgardt, University of Queensland
CoI: Remco van den Bosch, MPIA
CoI: Nadine Neumayer, ESO
CoI: Igor Chilingarian, Harvard-Smithsonian Center for Astrophysics
CoI: Richard McDermid, Macquarie University

Title: Resolving the Nature of Ultracompact Dwarfs

Abstract: 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.


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