Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Redshift Cutoff and the Quasar Epoch   We have obtained complete redshift information for a sample of 442 radio-loud
quasars with flux densities S(11cm) >= 0.25Jy. These come from a
completely-identified sample of 878 flat-spectrum radio sources, so there is no
optical magnitude limit. With these quasars, therefore, we can map out the
entire quasar epoch, unhindered by optical selection effects and any
intervening dust. The rapid decline in true space density above redshifts of
about 2.5 is confirmed. It agrees closely with that obtained from
optically-selected samples, indicating that these are also not significantly
affected by dust. The evolution of the quasar space density is similar to that
deduced for the global star formation rate, implying that the quasar epoch may
also be that of star formation. This sample of radio-selected quasars can now
be used in a variety of other studies, including unbiased searches for damped
Ly-alpha absorbers, studies of the phenomenon of ``red quasars'', and searches
for high-redshift molecular absorption systems.

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The categories of this paper are: acc-phys
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The categories of this paper are: hep-ex
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The categories of this paper are: solv-int
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: mtrl-th
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The categories of this paper are: cond-mat
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The categories of this paper are: chem-ph
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The categories of this paper are: funct-an
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The categories of this paper are: stat
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The categories of this paper are: nlin
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The categories of this paper are: cs
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The categories of this paper are: quant-ph