Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Environmental Influences on the Morphology and Dynamics of Group Size
  Haloes   We use group size haloes identified with a ``friends of friends'' (FOF)
algorithm in a concordance $\Lambda \rm{CDM}$ GADGET2 (dark matter only)
simulation to investigate the dependence of halo properties on the environment
at $z=0$. The study is carried out using samples of haloes at different
distances from their nearest massive {\em cluster} halo. We find that the
fraction of haloes with substructure typically increases in high density
regions. The halo mean axial ratio $<c/a>$ also increases in overdense regions,
a fact which is true for the whole range of halo mass studied. This can be
explained as a reflection of an earlier halo formation time in high-density
regions, which gives haloes more time to evolve and become more spherical.
Moreover, this interpretation is supported by the fact that, at a given
halo-cluster distance, haloes with substructure are more elongated than their
equal mass counterparts with no substructure, reflecting that the virialization
(and thus sphericalization) process is interrupted by merger events. The
velocity dispersion of low mass haloes with strong substructure shows a
significant increase near massive clusters with respect to equal mass haloes
with low-levels of substructure or with haloes found in low-density
environments. The alignment signal between the shape and the velocity ellipsoid
principal axes decreases going from lower to higher density regions, while such
an alignment is stronger for haloes without substructure. We also find, in
agreement with other studies, a tendency of halo major axes to be aligned and
of minor axes to lie roughly perpendicular with the orientation of the filament
within which the halo is embedded, an effect which is stronger in the proximity
of the massive clusters.

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The categories of this paper are: q-bio
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The categories of this paper are: solv-int
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The categories of this paper are: acc-phys
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The categories of this paper are: cond-mat
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The categories of this paper are: econ
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The categories of this paper are: quant-ph
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The categories of this paper are: eess
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
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The categories of this paper are: comp-gas
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The categories of this paper are: chao-dyn
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The categories of this paper are: math-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-th