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

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

2008-06-03

arxiv.org/abs/0806.0374v3

Astronomy and Astrophysics

Astrophysics

17 pages, 14 figures, accepted for publication in A&A. V3 taking into account proof corrections: Table 3 radial velocity entri

Scientific paper

10.1051/0004-6361:200810077

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

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