Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ionizing Photons and EUV Excesses in Clusters of Galaxies   Observations with the Extreme Ultraviolet Explorer satellite are purported to
show extreme ultraviolet (EUV) and soft X-ray excesses in several clusters of
galaxies (Bonamente, Lieu & Mittaz 2001). If interpreted as thermal emission,
this would imply the presence of warm (T\sim 10^6 K) gas in these clusters with
a mass comparable to that of gas at coronal temperatures. If true, this would
have profound implications for our understanding of galaxy clusters and the
distribution of baryons in the universe. Here we show that because of the large
ionizing photon emissivities of gas at such low temperatures, the ionizing
photon fluxes seen by disk galaxies in the observed clusters can be very large,
resulting in minimum emission measures from neutral gas in such disks as high
as 100 cm^(-6) pc. This result is essentially independent of the mechanism
actually responsible for producing the alleged EUV excesses. The predicted
emission measures in Abell 1795 (z=0.063) are about an order of magnitude
larger than seen in the Reynolds layer of the Galaxy, providing a
straightforward observational test of the reality of the EUV excess. New
tunable filter H alpha images and WFPC images from the Hubble Space Telescope
archive do not support the existence of the claimed EUV excess.

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The categories of this paper are: ao-sci
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
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The categories of this paper are: funct-an
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The categories of this paper are: mtrl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: eess
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The categories of this paper are: hep-th
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The categories of this paper are: hep-lat
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
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The categories of this paper are: nlin
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The categories of this paper are: hep-ex