Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical and Radio Properties of Extragalactic Sources Observed by the
  FIRST and SDSS Surveys   We discuss the optical and radio properties of 30,000 FIRST sources
positionally associated with an SDSS source in 1230 deg$^2$ of sky. The
majority (83%) of the FIRST sources identified with an SDSS source brighter
than r=21 are optically resolved. We estimate an upper limit of 5% for the
fraction of quasars with broad-band optical colors indistinguishable from those
of stars. The distribution of quasars in the radio flux -- optical flux plane
supports the existence of the "quasar radio-dichotomy"; 8% of all quasars with
i<18.5 are radio-loud and this fraction seems independent of redshift and
optical luminosity. The radio-loud quasars have a redder median color by 0.08
mag, and a 3 times larger fraction of objects with red colors. FIRST galaxies
represent 5% of all SDSS galaxies with r<17.5, and 1% for r<20, and are
dominated by red galaxies. Magnitude and redshift limited samples show that
radio galaxies have a different optical luminosity distribution than non-radio
galaxies selected by the same criteria; when galaxies are further separated by
their colors, this result remains valid for both blue and red galaxies. The
distributions of radio-to-optical flux ratio are similar for blue and red
galaxies in redshift-limited samples; this similarity implies that the
difference in their luminosity functions, and resulting selection effects, are
the dominant cause for the preponderance of red radio galaxies in flux-limited
samples. We confirm that the AGN-to-starburst galaxy number ratio increases
with radio flux, and find that radio emission from AGNs is more concentrated
than radio emission from starburst galaxies (abridged).

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The categories of this paper are: hep-th
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The categories of this paper are: math-ph
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The categories of this paper are: math
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The categories of this paper are: supr-con
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The categories of this paper are: gr-qc
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The categories of this paper are: quant-ph
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The categories of this paper are: cs
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an
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The categories of this paper are: q-fin
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The categories of this paper are: physics
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The categories of this paper are: hep-lat
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The categories of this paper are: q-bio
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The categories of this paper are: plasm-ph
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The categories of this paper are: funct-an
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The categories of this paper are: nlin