Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Galaxy Clusters in the Line of Sight to Background Quasars: I. Survey
  Design and Incidence of MgII Absorbers at Cluster Redshifts   We describe the first optical survey of absorption systems associated with
galaxy clusters at z= 0.3-0.9. We have cross-correlated SDSS DR3 quasars with
high-redshift cluster/group candidates from the Red-Sequence Cluster Survey. We
have found 442 quasar-cluster pairs for which the MgII doublet might be
detected at a transverse (physical) distance d<2 Mpc from the cluster centers.
To investigate the incidence (dN/dz) and equivalent-width distribution n(W) of
MgII systems at cluster redshifts, two statistical samples were drawn out of
these pairs: one made of high-resolution spectroscopic quasar observations (46
pairs), and one made of quasars used in MgII searches found in the literature
(375 pairs). The results are: (1) the population of strong MgII systems
(W_0>2.0 Ang.) near cluster redshifts shows a significant (>3 sigma)
overabundance (up to a factor of 15) when compared with the 'field' population;
(2) the overabundance is more evident at smaller distances (d<1 Mpc) than
larger distances (d<2 Mpc) from the cluster center; and, (3) the population of
weak MgII systems (W_0<0.3 Ang.) near cluster redshifts conform to the field
statistics. Unlike in the field, this dichotomy makes n(W) in clusters appear
flat and well fitted by a power-law in the entire W-range. A sub-sample of the
most massive clusters yields a stronger and still significant signal. Since
either the absorber number density or filling-factor/cross-section affects the
absorber statistics, an interesting possibility is that we have detected the
signature of truncated halos due to environmental effects. Thus, we argue that
the excess of strong systems is due to a population of absorbers in an
overdense galaxy environment, and the lack of weak systems to a different
population, that got destroyed in the cluster environment. (Abridged)

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The categories of this paper are: nucl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: q-bio
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The categories of this paper are: stat
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The categories of this paper are: chem-ph
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The categories of this paper are: math-ph
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The categories of this paper are: nlin
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The categories of this paper are: nucl-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ex
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The categories of this paper are: mtrl-th
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The categories of this paper are: solv-int
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The categories of this paper are: physics
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The categories of this paper are: econ
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The categories of this paper are: funct-an