Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Imagery and long-slit spectroscopy of the Polar-Ring Galaxy AM2020-504   Interactions between galaxies are very common. There are special kinds of
interactions that produce systems called Polar Ring Galaxies (PRGs), composed
by a lenticular, elliptical, or spiral host galaxy, surrounded by a ring of
stars and gas, orbiting in an approximately polar plane. The present work aims
to study AM2020-504, a PRG with an elliptical host galaxy, and a narrow and
well defined ring, probably formed by accretion of material from a donor
galaxy, collected by the host galaxy. Our observational study was based on BVRI
broad band imagery as well as longslit spectroscopy in the wavelenght range
4100--8600\AA, performed at the 1.6m telescope at the Observat\'orio do Pico
dos Dias (OPD), Brazil. We estimated a redshift of z= 0.01683, corresponding a
heliocentric radial velocity of 5045 +/-23 km/s. The (B-R) color map shows that
the ring is bluer than the host galaxy, indicating that the ring is a younger
structure. Standard diagnostic diagrams were used to classify the main ionizing
source of selected emission-line regions (nucleus, host galaxy and ring). It
turns out that the ring regions are mainly ionized by massive stars while the
nucleus presents AGN characteristics. Using two empirical methods, we found
oxygen abundances for the HII regions located in the ring in the range
12+log(O/H)=8.3-8.8 dex, the presence of an oxygen gradient across the ring,
and that AM2020-504 follows the metallicity-luminosity relation of spiral
galaxies. These results support the accretion scenario for this object and
rules out cold accretion as source for the HI gas in the polar ring.

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The categories of this paper are: patt-sol
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The categories of this paper are: bayes-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: mtrl-th
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The categories of this paper are: atom-ph
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The categories of this paper are: alg-geom
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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: solv-int
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The categories of this paper are: supr-con
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The categories of this paper are: hep-lat
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The categories of this paper are: gr-qc
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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: math
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The categories of this paper are: comp-gas