Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Active Galactic Nuclei in the Sloan Digital Sky Survey: I. Sample
  Selection   We have compiled a large sample of low-redshift active galactic nuclei (AGN)
identified via their emission line characteristics from the spectroscopic data
of the Sloan Digital Sky Survey. Since emission lines are often contaminated by
stellar absorption lines, we developed an objective and efficient method of
subtracting the stellar continuum from every galaxy spectrum before making
emission line measurements. The distribution of the measured H$\alpha$ Full
Width at Half Maxima values of emission line galaxies is strongly bimodal, with
two populations separated at about 1,200km s$^{-1}$. This feature provides a
natural separation between narrow-line and broad-line AGN. The narrow-line AGN
are identified using standard emission line ratio diagnostic diagrams. 1,317
broad-line and 3,074 narrow-line AGN are identified from about 100,000 galaxy
spectra selected over 1151 square degrees. This sample is used in a companion
paper to determine the emission-line luminosity function of AGN.

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The categories of this paper are: supr-con
18
The categories of this paper are: econ
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The categories of this paper are: adap-org
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The categories of this paper are: chem-ph
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The categories of this paper are: q-fin
3
The categories of this paper are: physics
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The categories of this paper are: plasm-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: cond-mat
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-th
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The categories of this paper are: q-alg
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The categories of this paper are: solv-int
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The categories of this paper are: math-ph
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The categories of this paper are: hep-th