Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The circum-galactic medium of quasars: CIV absorption systems   We investigate the properties of the circumgalactic gas in the halo of quasar
host galaxies from CIV absorption line systems. Optical spectroscopy of closely
aligned pairs of quasars (projected distance \leq 200 kpc) obtained at the Gran
Telescopio Canarias is used to investigate the distribution of the absorbing
gas for a sample of 18 quasars at z \sim 2. We found that the detected
absorption systems of EW \geq 0.3Ang associated with the foreground QSO are
revealed up to 200 kpc from the center of the host galaxy. The structure of the
absorbing gas is rather patchy with a covering fraction of the gas that quickly
decreases beyond 100 kpc. These results are in qualitative agreement with those
found for the lower ionisation metal Mg II 2800 Ang.

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The categories of this paper are: math
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The categories of this paper are: plasm-ph
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The categories of this paper are: physics
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The categories of this paper are: atom-ph
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The categories of this paper are: supr-con
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: q-alg
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The categories of this paper are: alg-geom
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The categories of this paper are: cs
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The categories of this paper are: hep-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: funct-an
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The categories of this paper are: solv-int