Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Outer Regions of the Cluster Gaseous Atmospheres   We present a systematic study of the hot gas distribution in the outer
regions of regular clusters using ROSAT PSPC data. Outside the cooling flow
region, the beta-model describes the observed surface brightness closely, but
not precisely. Between 0.3 and 1 virial radii, the profiles are characterized
by a power law with slope, expressed in terms of the beta parameter, in the
range beta=0.65 to 0.85. The values of beta in this range of radii are
typically larger by ~0.05 than those derived from the global fit. There is a
mild trend for the slope to increase with temperature, from <beta>~0.68 for 3
keV clusters to ~0.8 for 10 keV clusters; however, even at high temperatures
there are clusters with flat gas profiles, 0.7. Our values of beta at large
radius are systematically higher, and the trend of beta with temperature is
weaker than was previously found; the most likely explanation is that earlier
studies were affected by an incomplete exclusion of the central cooling flow
regions. For our regular clusters, the gas distribution at large radii is quite
close to spherically symmetric and this is shown not to be an artifact of the
sample selection. The gas density profiles are very similar when compared in
the units of cluster virial radius. The radius of fixed mean gas overdensity
1000 (corresponding to the dark matter overdensity 200 for Omega=0.2) shows a
tight correlation with temperature, R~T**0.5, as expected from the virial
theorem for clusters with the universal gas fraction. At a given temperature,
the rms scatter of the gas overdensity radius is only ~7% which translates into
a 20% scatter of the gas mass fraction, including statistical scatter due to
measurement uncertainties.

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The categories of this paper are: eess
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
30
The categories of this paper are: q-alg
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The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
10
The categories of this paper are: q-bio
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The categories of this paper are: math-ph
2
The categories of this paper are: math
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The categories of this paper are: chao-dyn
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The categories of this paper are: comp-gas
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-fin
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The categories of this paper are: hep-lat