Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: IC 225: a dwarf elliptical galaxy with a peculiar blue core   We present the discovery of a peculiar blue core in the elliptical galaxy IC
225 by using images and spectrum from the Sloan Digital Sky Survey (SDSS). The
outer parts of the surface brightness profiles of u-, g-, r-, i- and z-band
SDSS images for IC 225 are well fitted with an exponential function. The
fitting results show that IC 225 follows the same relations between the
magnitude, scale length and central surface brightness for dwarf elliptical
galaxies. Its absolute blue magnitude (M_B) is -17.14 mag, all of which suggest
that IC 225 is a typical dwarf elliptical galaxy. The g-r color profile
indicates a very blue core with a radius of 2 arcseconds, which is also clearly
seen in the RGB image made of g-, r- and i-band SDSS images. The SDSS optical
spectrum exhibits strong and very narrow nebular emission lines. The metal
abundances derived by the standard methods, which are 12+log(O/H) = 8.98,
log(N/O) = -0.77 and 12+log(S+/H+) = 6.76, turn out to be significantly higher
than that predicted by the well-known luminosity-metallicity relation. After
carefully inspecting the central region of IC 225, we find that there are two
distinct nuclei, separated by 1.4 arcseconds, the off-nucleated one is even
bluer than the nucleus of IC 225. The asymmetric line profiles of higher-order
Balmer lines indicate that the emission lines are bluer shifted relative to the
absorption lines, suggesting that the line emission arises from the off-center
core, whose nature is a metal-rich Hii region. To the best of our knowledge, it
is the first high-metallicity Hii region detected in a dwarf elliptical galaxy.

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The categories of this paper are: econ
2
The categories of this paper are: math
16
The categories of this paper are: stat
3
The categories of this paper are: physics
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The categories of this paper are: chem-ph
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The categories of this paper are: solv-int
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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: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: nlin
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The categories of this paper are: q-fin
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-ph