Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Graininess of Dark Matter Haloes   We use the recently completed one billion particle Via Lactea II LambdaCDM
simulation to investigate local properties like density, mean velocity,
velocity dispersion, anisotropy, orientation and shape of the velocity
dispersion ellipsoid, as well as structure in velocity space of dark matter
haloes. We show that at the same radial distance from the halo centre, these
properties can deviate by orders of magnitude from the canonical, spherically
averaged values, a variation that can only be partly explained by triaxiality
and the presence of subhaloes. The mass density appears smooth in the central
relaxed regions but spans four orders of magnitude in the outskirts, both
because of the presence of subhaloes as well as of underdense regions and holes
in the matter distribution. In the inner regions the local velocity dispersion
ellipsoid is aligned with the shape ellipsoid of the halo. This is not true in
the outer parts where the orientation becomes more isotropic. The clumpy
structure in local velocity space of the outer halo can not be well described
by a smooth multivariate normal distribution. Via Lactea II also shows the
presence of cold streams made visible by their high 6D phase space density.
Generally, the structure of dark matter haloes shows a high degree of
graininess in phase space that cannot be described by a smooth distribution
function.

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The categories of this paper are: nucl-ex
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The categories of this paper are: supr-con
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The categories of this paper are: hep-ex
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The categories of this paper are: econ
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The categories of this paper are: math
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The categories of this paper are: hep-lat
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: quant-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: mtrl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: q-alg
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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol