Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Nature of UCDs: Internal Dynamics from an Expanded Sample and
  Homogeneous Database   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<M/M_*<10^8), using
FLAMES/Giraffe at the VLT. This is the largest homogeneous data set of UCD
internal dynamics assembled to date. We derive dynamical M/L ratios for 15 UCDs
covered by HST imaging. In the M_V-sigma plane, UCDs with M_V<-12 mag are
consistent with the extrapolated Faber-Jackson relation for luminous
ellipticals, while fainter UCDs are closer to the extrapolated globular cluster
(GC) relation. At a given metallicity, Fornax UCDs have on average 30-40% lower
M/L ratios than Virgo UCDs, suggesting possible differences in age or dark
matter content between Fornax and Virgo UCDs. For our sample of Fornax UCDs we
find no significant correlation between M/L ratio and mass. We combine our data
with available M/L ratio measurements of compact stellar systems with
10^4<M/M_*<10^8, and normalise all M/L estimates to solar metallicity. We find
that UCDs (M > 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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The categories of this paper are: physics
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The categories of this paper are: mtrl-th
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The categories of this paper are: adap-org
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The categories of this paper are: stat
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-ph
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The categories of this paper are: math
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The categories of this paper are: quant-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: math-ph
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The categories of this paper are: solv-int
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The categories of this paper are: q-fin
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The categories of this paper are: hep-lat
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The categories of this paper are: patt-sol
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The categories of this paper are: supr-con
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The categories of this paper are: econ