Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First Results from a Photometric Survey of Strong Gravitational Lens
  Environments   Many strong gravitational lenses lie in complex environments, such as poor
groups of galaxies, that significantly bias conclusions from lens analyses. We
are undertaking a photometric survey of all known galaxy-mass strong lenses to
characterize their environments and include them in careful lens modeling, and
to build a large, uniform sample of galaxy groups at intermediate redshifts for
evolutionary studies. In this paper we present wide-field photometry of the
environments of twelve lens systems with 0.24 < z_lens < 0.5. Using a
red-sequence identifying technique, we find that eight of the twelve lenses lie
in groups, and that ten group-like structures are projected along the line of
sight towards seven of these lenses. Follow-up spectroscopy of a subset of
these fields confirms these results. For lenses in groups, the group centroid
position is consistent with the direction of the external tidal shear required
by lens models. Lens galaxies are not all super-L_* ellipticals; the median
lens luminosity is < L_*, and the distribution of lens luminosities extends 3
magnitudes below L_* (in agreement with theoretical models). Only two of the
lenses in groups are the brightest group galaxy, in qualitative agreement with
theoretical predictions. As in the local Universe, the highest
velocity-dispersion groups contain a brightest member spatially coincident with
the group centroid, whereas lower-dispersion groups tend to have an offset
brightest group galaxy. This suggests that higher-dispersion groups are more
dynamically relaxed than lower-dispersion groups and that at least some evolved
groups exist by z ~ 0.5.

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The categories of this paper are: gr-qc
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The categories of this paper are: ao-sci
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The categories of this paper are: q-bio
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The categories of this paper are: q-fin
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The categories of this paper are: atom-ph
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The categories of this paper are: funct-an
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The categories of this paper are: q-alg
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The categories of this paper are: quant-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: nlin
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The categories of this paper are: patt-sol
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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: comp-gas
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The categories of this paper are: chao-dyn
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The categories of this paper are: cs