Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The ROSAT Brightest Cluster Sample (BCS) - I. The compilation of the
  sample and the cluster log N-log S distribution   We present a 90 per cent flux-complete sample of the 201 X-ray brightest
clusters of galaxies in the northern hemisphere (dec > 0 deg), at high Galactic
latitudes (|b| > 20 deg), with measured redshifts z < 0.3 and fluxes higher
than 4.4 x 10^(-12) erg cm^(-2) s^{-1) in the 0.1-2.4 keV band. The sample,
called the ROSAT Brightest Cluster Sample (BCS), is selected from ROSAT All-Sky
Survey data and is the largest X-ray selected cluster sample compiled to date.
In addition to Abell clusters, which form the bulk of the sample, the BCS also
contains the X-ray brightest Zwicky clusters and other clusters selected from
their X-ray properties alone. Effort has been made to ensure the highest
possible completeness of the sample and the smallest possible contamination by
non-cluster X-ray sources. X-ray fluxes are computed using an algorithm
tailored for the detection and characterization of X-ray emission from galaxy
clusters. These fluxes are accurate to better than 15 per cent (mean 1 sigma
error).
  We find the cumulative log N-log S distribution of clusters to follow a power
law k S^(-alpha) with alpha=1.31 (+0.06)(-0.03) (errors are the 10th and 90th
percentiles) down to fluxes of 2 x 10^(-12) erg cm^(-2) s^(-1), i.e.
considerably below the BCS flux limit. Although our best-fitting slope
disagrees formally with the canonical value of -1.5 for a Euclidean
distribution, the BCS log N-log S distribution is consistent with a
non-evolving cluster population if cosmological effects are taken into account.

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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: cond-mat
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The categories of this paper are: eess
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The categories of this paper are: adap-org
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The categories of this paper are: hep-th
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The categories of this paper are: comp-gas
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: math
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The categories of this paper are: alg-geom
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The categories of this paper are: mtrl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: gr-qc
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The categories of this paper are: cs