Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The GEMS project: X-ray analysis and statistical properties of the group
  sample   The GEMS project involves a multi-wavelength study of a sample of 60 galaxy
groups. Substantial ROSAT PSPC observations are used to characterise the state
of the intergalactic medium in each. We present the results of a uniform
analysis of these ROSAT data, and a statistical investigation of the
relationship between X-ray and optical properties across the sample. The
steepening of the LX-TX relation in the group regime reported previously is not
seen in our sample, which fits well onto the cluster trend. A number of biases
affect the fitting of regression lines under these circumstances, and until the
impact of these has been thoroughly investigated it seems best to regard the
slope of the group LX-TX relation as being poorly determined. A significant
problem in comparing the properties of groups and clusters is the derivation of
system radii, to allow different systems to be compared within regions having
the same overdensity. We find evidence that group velocity dispersion provides
a very unreliable measure of system mass (and hence radius), with a number of
groups having remarkably low values of sigma. We confirm that the surface
brightness profiles of groups are significantly flatter than those of clusters,
however we find no significant tendency within our sample for cooler groups to
show flatter profiles. This result is inconsistent with simple universal
preheating models. The morphology of the galaxies in the GEMS groups is
correlated to their X-ray properties in a number of ways: we confirm the very
strong relationship between X-ray emission and a dominant early-type central
galaxy, and also find that spiral fraction is correlated with the temperature
of the hot gas. A class of spiral-rich groups with little or no X-ray emission,
probably corresponds to groups which have not yet fully collapsed.

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The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
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: bayes-an
4
The categories of this paper are: cond-mat
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The categories of this paper are: hep-th
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The categories of this paper are: acc-phys
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The categories of this paper are: comp-gas
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The categories of this paper are: adap-org
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
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The categories of this paper are: dg-ga
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The categories of this paper are: mtrl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: eess