Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Serendipitous discovery of a cluster of galaxies with a peculiar central
  galaxy   We report the serendipitous discovery of a cluster of galaxies at z=0.369.
Thirty-eight candidate members were identified based on rough broad-band
photometric redshifts, and three members were confirmed spectroscopically. The
brightest cluster galaxy (BCG) is exceptionally blue, with B-V=0.12 and
V-I=1.02. The surface-brightness profile of the BCG follows an r^(1/4)-law
profile out to 3" in all three bands. The effective radius is significantly
smaller in bluer bandpasses, resulting in a blue core and a color gradient
opposite to the metallicity-induced color gradient observed in typical
elliptical galaxies. Beyond 3" an extended envelope of emission in excess of
the r^(1/4)-law profile is observed, the position angle of which coincides with
the major axis of the galaxy cluster. The spectrum of the BCG contains strong
Balmer absorption, a minimal 4000 A break, and a broad Mg II emission line,
suggesting that the galaxy has undergone recent star formation and may harbor a
central AGN. The presence of numerous nearby bright stars makes this cluster an
interesting target for next-generation adaptive optics using natural guide
stars.

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The categories of this paper are: alg-geom
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
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The categories of this paper are: eess
29
The categories of this paper are: funct-an
32
The categories of this paper are: atom-ph
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
18
The categories of this paper are: econ
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph