Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The flat oxygen abundance gradient in the extended disk of M83   We have obtained deep multi-object optical spectra of 49 HII regions in the
outer disk of the spiral galaxy M83 (=NGC 5236) with the FORS2 spectrograph at
the Very Large Telescope. The targets span the range in galactocentric distance
between 0.64 and 2.64 times the R25 isophotal radius (5.4-22.3 kpc), and 31 of
them are located at R>R25, thus belonging to the extreme outer disk of the
galaxy, populated by UV complexes revealed recently by the GALEX satellite. In
order to derive the nebular chemical abundances, we apply several diagnostics
of the oxygen abundance, including R23, [NII]/[OII] and the [OIII]4363 auroral
line, which was detected in four HII regions. We find that, while inwards of
the optical edge the O/H ratio follows the radial gradient known from previous
investigations, the outer abundance trend flattens out to an approximately
constant value. The latter varies, according to the adopted diagnostic, between
12+log(O/H)=8.2 and 12+log(O/H)=8.6 (i.e. from approximately 1/3 the solar
oxygen abundance to nearly the solar value). An abrupt discontinuity in the
radial oxygen abundance trend is also detected near the optical edge of the
disk. These results are tentatively linked to the flat gas surface density in
the outskirts of the galaxy, the relatively unevolved state of the extended
disk of M83, and the redistribution of chemically enriched gas following a past
galaxy encounter.

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The categories of this paper are: nlin
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-alg
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The categories of this paper are: patt-sol
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The categories of this paper are: supr-con
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The categories of this paper are: nucl-th
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The categories of this paper are: q-fin
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The categories of this paper are: stat
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The categories of this paper are: math
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The categories of this paper are: econ
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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: hep-th
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The categories of this paper are: chem-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: cond-mat