Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Origin of X-shaped radio-sources: further insights from the properties
  of their host galaxies   We analyze the properties of a sample of X-shaped radio-sources (XRSs). These
objects show, in addition to the main lobes, a pair of wings producing their
peculiar radio morphology. We obtain our sample by selecting from the initial
list of Cheung (2007, AJ, 133, 2097) the 53 galaxies with the better defined
wings and with available SDSS images. We identified the host galaxies and
measured their optical position angle, obtaining a positive result in 22 cases.
The orientation of the secondary radio structures shows a strong connection
with the optical axis, with all (but one) wing forming a angle larger than 40
degrees with the host major axis. The probability that this is compatible with
a uniform distribution is P = 0.9 10E-4. Spectra are available from the SDSS
for 28 XRSs. We modeled them to extract information on their emission lines and
stellar population properties. The sample is formed by approximately the same
number of high and low excitation galaxies (HEG and LEG); this classification
is essential for a proper comparison with non-winged radio-galaxies. XRSs
follow the same relations between radio and line luminosity defined by
radio-galaxies in the 3C sample. While in HEGs a young stellar population is
often present, this is not detected in the 13 LEGs, again in agreement with the
properties of non XRSs. The lack of young stars in LEGs support the idea that
they did not experiences a recent gas rich merger. The connection between the
optical axis and the wings orientation, as well as the stellar population and
emission lines properties, provide further support for an hydro-dynamic origin
of the radio-wings (for example associated with the expansion of the radio
cocoon in an asymmetric external medium) rather than with a change of
orientation of the jet axis.

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The categories of this paper are: ao-sci
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The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: eess
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The categories of this paper are: nlin
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The categories of this paper are: acc-phys
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The categories of this paper are: stat
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The categories of this paper are: cs
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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: chem-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-lat
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The categories of this paper are: solv-int