Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The 9.7 Micron Silicate Dust Absorption Toward the Cygnus A Nucleus and
  the Inferred Location of the Obscuring Dust   We report the detection of a 9.7 $\mu$m silicate dust absorption feature
toward the Cygnus A nucleus. Its optical depth is, however, significantly
smaller than that expected from the dust extinction toward the background
$L$-band emission region ($A_{\rm V}$ $\sim$ 150 mag). We argue that the most
likely explanation for the small optical depth is that the obscuring dust
exists so close to the central engine that a temperature gradient occurs. Our
calculation confirms that the small optical depth and the spectral energy
distribution at 3--30 $\mu$m can be quantitatively reproduced by this
explanation. Combining this picture with the huge AGN luminosity, the emission
properties of Cygnus A are consistent with those of a type 2 quasar, that is, a
highly luminous AGN that is highly obscured ($A_{\rm V}$ $>$ 50 mag) by a dusty
torus with an inner radius of $<$10 pc, and not by $>$ a few 100 pc scale dust
in the host galaxy.

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The categories of this paper are: hep-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: physics
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-ph
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The categories of this paper are: cs
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The categories of this paper are: quant-ph
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The categories of this paper are: eess
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The categories of this paper are: acc-phys
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The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
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The categories of this paper are: gr-qc
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The categories of this paper are: q-alg
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The categories of this paper are: nucl-ex
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The categories of this paper are: econ
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The categories of this paper are: ao-sci