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arXiv · 0806.0374

The Nature of UCDs: Internal Dynamics from an Expanded Sample and Homogeneous Database

Steffen Mieske·Michael Hilker·Andres Jordan·Leopoldo Infante·Markus Kissler-Patig·Marina Rejkuba·Tom Richtler·Patrick Cote·Holger Baumgardt·Michael J. West·Laura Ferrarese·Eric W. Peng
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Abstract

We have obtained high-resolution spectra of 23 ultra-compact dwarf galaxies (UCDs) in the Fornax cluster with -10.4>M_V>-13.5 mag (10^6 2*10^6 M_*) have M/L ratios twice as large as GCs (M < 2*10^6 M_*). We show that stellar population models tend to under-predict dynamical M/L ratios of UCDs and over-predict those of GCs. Considering the scaling relations of stellar spheroids, UCDs align well along the 'Fundamental Manifold', constituting the small-scale end of the galaxy sequence. The alignment for UCDs is especially clear for r_e >~ 7 pc, which corresponds to dynamical relaxation times that exceed a Hubble time. In contrast, GCs exhibit a broader scatter and do not appear to align along the manifold. We argue that UCDs are the smallest dynamically un-relaxed stellar systems, with M > 2*10^6 M_* and 7<r_e<100 pc. Future studies should aim at explaining the elevated M/L ratios of UCDs and the environmental dependence of their properties.

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Steffen Mieske, Michael Hilker, Andres Jordan, Leopoldo Infante, Markus Kissler-Patig, Marina Rejkuba, Tom Richtler, Patrick Cote, Holger Baumgardt, Michael J. West, Laura Ferrarese, Eric W. Peng. 2008-06-03. The Nature of UCDs: Internal Dynamics from an Expanded Sample and Homogeneous Database. https://doi.org/10.1051/0004-6361:200810077

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