Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: CASSOWARY 20: a Wide Separation Einstein Cross Identified with the
  X-shooter Spectrograph   We have used spectra obtained with X-shooter, the triple arm optical-infrared
spectrograph recently commissioned on the Very Large Telescope of the European
Southern Observatory, to confirm the gravitational lens nature of the CASSOWARY
candidate CSWA 20. This system consists of a luminous red galaxy at redshift
z(abs) = 0.741, with a very high velocity dispersion sigma(lens) = 500 km/s,
which lenses a blue star-forming galaxy at z(em) = 1.433 into four images with
mean separation of about 6 arcseconds. The source shares many of its properties
with those of UV-selected galaxies z = 2-3: it is forming stars at a rate of 25
solar masses per year, has a metallicity of about 1/4 solar, and shows nebular
emission from two components separated by 0.4 arcseconds in the image plane,
possibly indicating a merger. It appears that foreground interstellar material
within the galaxy has been evacuated from the sight-line along which we observe
the starburst, giving an unextinguished view of its stars and H II regions.
CSWA 20, with its massive lensing galaxy producing a high magnification of an
intrinsically luminous background galaxy, is a promising target for future
studies at a variety of wavelengths.

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The categories of this paper are: math
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The categories of this paper are: hep-lat
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-alg
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The categories of this paper are: hep-ph
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The categories of this paper are: adap-org
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The categories of this paper are: nlin
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The categories of this paper are: econ
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The categories of this paper are: physics
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The categories of this paper are: cmp-lg
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The categories of this paper are: alg-geom
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The categories of this paper are: gr-qc
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The categories of this paper are: math-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-ex
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The categories of this paper are: mtrl-th