Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fossil Systems in the 400d Cluster Catalog   We report the discovery of seven new fossil systems in the 400d cluster
survey. Our search targets nearby, $z\le0.2$, and X-ray bright, $L_X\ge
10^{43}$ erg sec$^{-1}$, clusters of galaxies. Where available, we measure the
optical luminosities from Sloan Digital Sky Survey images, thereby obtaining
uniform sets of both X-ray and optical data. Our selection criteria identify 12
fossil systems, out of which five are known from previous studies. While in
general agreement with earlier results, our larger sample size allows us to put
tighter constraints on the number density of fossil clusters. It has been
previously reported that fossil groups are more X-ray bright than other X-ray
groups of galaxies for the same optical luminosity. We find, however, that the
X-ray brightness of massive fossil systems is consistent with that of the
general population of galaxy clusters and follows the same $L_X-L_{\rm opt}$
scaling relation.

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The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: stat
0
The categories of this paper are: hep-ph
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The categories of this paper are: cs
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The categories of this paper are: hep-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: math-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: q-fin