Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Low-Ionization Emission Regions in Quasars: Gas Properties Probed with
  Broad O I and Ca II Lines   We have compiled the emission-line fluxes of O I 8446, O I 11287, and the
near-IR Ca II triplet (8579) observed in 11 quasars. These lines are considered
to emerge from the same gas as do the Fe II lines in the low-ionized portion of
the broad emission line region (BELR). The compiled quasars are distributed
over wide ranges of redshift (0.06 < z < 1.08) and of luminosity (-29.8 < M_B <
-22.1), thus representing a useful sample to investigate the line-emitting gas
properties in various quasar environments. The measured line strengths and
velocities, as functions of the quasar properties, are analyzed using
photoionization model calculations. We found that the flux ratio between Ca II
and O I 8446 is hardly dependent on the redshift or luminosity, indicating
similar gas density in the emission region from quasar to quasar. On the other
hand, a scatter of the O I 11287/8446 ratios appears to imply the diversity of
the ionization parameter. These facts invoke a picture of the line-emitting
gases in quasars that have similar densities and are located at regions exposed
to various ionizing radiation fluxes. The observed O I line widths are found to
be remarkably similar over more than 3 orders of magnitude in luminosity, which
indicates a kinematically determined location of the emission region and is in
clear contrast to the well-studied case of H I lines. We also argue about the
dust presence in the emission region since the region is suggested to be
located near the dust sublimation point at the outer edge of the BELR.

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The categories of this paper are: stat
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-th
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The categories of this paper are: math-ph
33
The categories of this paper are: plasm-ph
30
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: hep-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: q-bio
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
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The categories of this paper are: cond-mat