Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Approaching Reionization: The Evolution of the Lyman Alpha Forest from
  Redshifts Four to Six   We analyze the Ly alpha forest properties of a sample of 15 high redshift
quasars lying between z = 4.42 and z = 5.75, using high signal-to-noise spectra
obtained with ESI on the Keck II 10 m telescope. The distribution of
transmissions in the Ly alpha region in this redshift range is shown to be
consistent with that found in lambda cold dark matter simulations with a
smoothly evolving ionization rate as a function of redshift. The extrapolation
of the ionizing flux to z = 6.05 lies a factor of two higher than a 2 sigma
upper limit placed by Cen & McDonald (2001) at this redshift, based on the
Becker et al. (2001) spectra of the z = 6.28 quasar SDSS 1030+0524. However,
the data are also consistent with models in which there is substantial
variation of the ionization parameter about the mean value, and in this case,
dark gaps such as those seen by Becker et al. become much more likely. We
conclude that further data are needed before we can be sure that we have seen
the epoch of reionization. We also summarize the damped Ly alpha systems seen
in these quasar lines of sight and measure their metallicities and kinematic
properties. We argue that the mean DLA metallicity has dropped substantially by
z = 5 compared with its value at z < 4.

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The categories of this paper are: math
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The categories of this paper are: bayes-an
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-lat
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The categories of this paper are: acc-phys
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The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-ex
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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: mtrl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ph
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The categories of this paper are: math-ph