Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The SDSS-DR5 Survey for Proximate Damped Lya Systems   Using the Sloan Digital Sky Survey, Data Release 5, we survey proximate
damped Lya systems (PDLAs): absorption line systems with HI column density
N(HI)> 2x10^20 cm^{-2} at velocity separation dv < 3000 km/s from their
background quasar. These absorbers are physically associated with their
background quasars, and their statistics allow us to study quasar environments
out to z~5. However, the large ionizing flux emitted by a quasar can ionize the
neutral gas in a nearby galaxy possibly giving rise to a ``proximity effect'',
analogous to the similar effect observed in the Lya forest. From a sample of
111 PDLAs, we measure the HI frequency distribution f(N), incidence, and gas
mass density of the PDLAs near luminous quasars over the redshift interval z=
2.2 to 5. The incidence and mass density of PDLAs at z~3 is approximately twice
that of intervening DLAs, but at z<2.5 and z>3.5 the f(N) distribution is
consistent with the intervening population. We interpret the observed
enhancement of PDLAs around quasars in terms of quasar-galaxy clustering, and
compare the strength of the clustering signal to the expectation from
independent measures of the respective clustering strengths of DLAs and
quasars, as well as a complementary analysis of the clustering of absorbers
around quasars in the transverse direction. We find that there are a factor of
5-10 fewer PDLAs around quasars than expected and interpret this result as
evidence for the hypothesis that the ionizing flux from the quasars
photoevaporates HI in nearby DLA galaxies, thus reducing their cross-section
for DLA absorption. This constitues the first detection of a ``proximity
effect'' for DLAs.

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The categories of this paper are: bayes-an
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The categories of this paper are: chem-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: supr-con
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The categories of this paper are: gr-qc
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The categories of this paper are: physics
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: eess
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The categories of this paper are: alg-geom
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: q-alg
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The categories of this paper are: mtrl-th