Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Highly polarized structures in the near-nuclear regions of Cygnus A:
  intrinsic anisotropy within the cones?   We present near-IR imaging polarimetry observations of the nucleus of Cygnus
A, taken with the NICMOS camera of the HST at a wavelength of 2.0 microns.These
maps reveal a highly collimated region of polarized emission straddling the
nucleus and extending to a radius of 1.2 arcseconds. Remarkably, this feature
coincides with one, but only one, limb of the edge-brightened bicone structure
seen in the total intensity image. The high degree (P_k ~ 25%) and orientation
of the extended polarization feature are consistent with a scattering origin.
Most plausibly, the detection of polarization along only one limb of the bicone
is a consequence of intrinsic anisotropy of the near-IR continuum within the
radiation cones, with the direction of maximum intensity of the near-IR
radiation field significantly displaced from the direction of the radio axis.
The unresolved nuclear core source is also highly polarized (P_k > 28%), with a
position angle close to the perpendicular to the radio axis. Given that this
high degree of nuclear polarization can only be explained in terms of dichroic
extinction if the dichroic mechanism is unusually efficient in Cygnus A, it is
more likely that the nuclear polarization is due to the scattering of nuclear
light in an unresolved scattering region close to the AGN. In this case, the
flux of the core source in the K-band is dominated by scattered rather than
transmitted quasar light, and previous extinction estimates based on K-band
photometry of the core substantially underestimate the true nuclear extinction.

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The categories of this paper are: ao-sci
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The categories of this paper are: mtrl-th
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The categories of this paper are: adap-org
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The categories of this paper are: quant-ph
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The categories of this paper are: q-fin
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The categories of this paper are: supr-con
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The categories of this paper are: bayes-an
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The categories of this paper are: chem-ph
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The categories of this paper are: comp-gas
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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: hep-ex
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The categories of this paper are: cs
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The categories of this paper are: econ
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph