Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Multiphase Intergalactic Medium towards PKS 2155-304   We study the cluster of H I and O VI absorption systems and the claimed
detection of O VIII absorption from the intergalactic medium at z ~ 0.0567,
associated with a group of galaxies toward the BL Lac object PKS 2155-304. As
measured by spectrographs on the Hubble Space Telescope, Far Ultraviolet
Spectroscopic Explorer, and Chandra, this system appears to contain gas at a
variety of temperatures. We analyze this multi-phase gas in a clumpy-infall
model. From the absence of C IV and Si III absorption in the Ly-alpha clouds,
we infer metallicities less than 2.5-10% of solar values. The only metals are
detected in two O VI absorption components, offset by +/- 400 km/s from the
group barycenter (cz ~ 16,600 km/s). The O VI components may signify "nearside"
and "backside" infall into the group potential well, which coincides with the
claimed O VIII absorption. If the claimed O VIII detection is real, our
analysis suggests that clusters of strong Ly-alpha and O VI absorbers,
associated with groups of galaxies, may be the "signposts" of shock-heated,
metal-enriched baryons. Through combined UV and X-ray spectra of H I and O VI,
O VII, and O VIII, one may be able to clarify the heating mechanism of this
multiphase gas.

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The categories of this paper are: quant-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ex
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The categories of this paper are: q-fin
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: gr-qc
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The categories of this paper are: funct-an
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-alg
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The categories of this paper are: cmp-lg
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The categories of this paper are: chao-dyn
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The categories of this paper are: ao-sci
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The categories of this paper are: dg-ga
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The categories of this paper are: acc-phys