Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Precious Metals in SDSS Quasar Spectra I: Tracking the Evolution of
  Strong, 1.5 < z < 4.5 CIV Absorbers with Thousands of Systems   We have vastly increased the CIV statistics at intermediate redshift by
surveying the thousands of quasars in the Sloan Digital Sky Survey Data-Release
7. We visually verified over 16,000 CIV systems with 1.46 < z < 4.55---a sample
size that renders Poisson error negligible. Detailed Monte Carlo simulations
show we are approximately 50% complete down to rest equivalent widths W_r ~ 0.6
\AA. We analyzed the sample as a whole and in ten small redshift bins with
approximately 1500 doublets each. The equivalent width frequency distributions
f(W_r) were well modeled by an exponential, with little evolution in shape. In
contrast with previous studies that modeled the frequency distribution as a
single power law, the fitted exponential gives a finite mass density for the
CIV ions. The co-moving line density dN_CIV/dX evolved smoothly with redshift,
increasing by a factor of 2.37+/-0.09 from z = 4.55 to 1.96, then plateauing at
dN_CIV/dX ~ 0.34 for z = 1.96 to 1.46. Comparing our SDSS sample with z < 1
(ultraviolet) and z > 5 (infrared) surveys, we see an approximately 10-fold
increase in dN_CIV/dX over z ~ 6 --> 0, for W_r >= 0.6 \AA. This suggests a
monotonic and significant increase in the enrichment of gas outside galaxies
over the 12 Gyr lifetime of the universe.

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The categories of this paper are: comp-gas
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The categories of this paper are: math-ph
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The categories of this paper are: alg-geom
4
The categories of this paper are: cond-mat
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-fin
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The categories of this paper are: eess
1
The categories of this paper are: cs
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The categories of this paper are: chem-ph
7
The categories of this paper are: hep-th
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The categories of this paper are: q-bio
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The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-th