Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 4C +12.50: A Superluminal Precessing Jet in the Recent Merger System
  IRAS 13451+1232   We present the results of a multi-epoch VLBA study of the powerful radio
source 4C +12.50 (PKS 1345+125) at a wavelength of 2 cm. This compact radio
source is associated with a hidden quasar whose host galaxy shows signs of a
recent merger. It has been classified as a compact symmetric source (CSO) due
to its small overall size (~220 pc) and twin-jet morphology, although it also
has faint extended emission that may be a relic of previous activity. We report
the detection of exceedingly high linear fractional polarization in isolated
features of the southern jet (up to 60%), which is highly unusual for a CSO.
Given the large amount of gas present in the host galaxy, we would expect
significant Faraday depolarization across the whole source, unless the
depolarizing gas is fairly clumpy. The southern jet also contains two features
that are moving outward from the core at apparent speeds of v/c = 1.0 +/- 0.3
and 1.2 +/- 0.3. These represent the first positive detections of superluminal
motion in a CSO, and taken together with the jet to counter-jet flux ratio,
suggest an intrinsic flow speed of v/c = 0.84 +/- 0.12. The apparent ridgeline
of the jet and counter-jet are consistent with a conical helix of wavelength
280 pc that is the result of Kelvin-Helmholtz instabilities driven by a slow
precession of the jet nozzle. A fit to the data implies that the nozzle is
precessing around a cone with half-angle 23 degrees, whose axis lies at an
angle of 82 degrees to the line of sight. We suggest that the "S"-shaped jet
morphologies commonly seen in recent AGN outflows such as 4C +12.50 may simply
reflect the fact that their black hole spin axes are still precessing, and have
not had sufficient time to align with their accretion disks.

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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: q-alg
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The categories of this paper are: nlin
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The categories of this paper are: hep-lat
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The categories of this paper are: math-ph
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The categories of this paper are: cs
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The categories of this paper are: solv-int
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ph
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The categories of this paper are: supr-con
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The categories of this paper are: ao-sci
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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: funct-an
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The categories of this paper are: cmp-lg