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|a Wong, Ka-Wah
|e author
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|a MIT Kavli Institute for Astrophysics and Space Research
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|a Ji, Li
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|a Sarazin, Craig L.
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|a Ji, Li
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|a X-RAY SIGNATURES OF NON-EQUILIBRIUM IONIZATION EFFECTS IN GALAXY CLUSTER ACCRETION SHOCK REGIONS
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|b IOP Publishing,
|c 2015-02-25T21:02:40Z.
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|z Get fulltext
|u http://hdl.handle.net/1721.1/95634
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|a The densities in the outer regions of clusters of galaxies are very low, and the collisional timescales are very long. As a result, heavy elements will be under-ionized after they have passed through the accretion shock. We have studied systematically the effects of non-equilibrium ionization for relaxed clusters in the ΛCDM cosmology using one-dimensional hydrodynamic simulations. We found that non-equilibrium ionization effects do not depend on cluster mass, but depend strongly on redshift which can be understood by self-similar scaling arguments. The effects are stronger for clusters at lower redshifts. We present X-ray signatures such as surface brightness profiles and emission lines in detail for a massive cluster at low redshift. In general, soft emission (0.3-1.0 keV) is enhanced significantly by under-ionization, and the enhancement can be nearly an order of magnitude near the shock radius. The most prominent non-equilibrium ionization signature we found is the O VII and O VIII line ratio. The ratios for non-equilibrium ionization and collisional ionization equilibrium models are different by more than an order of magnitude at radii beyond half of the shock radius. These non-equilibrium ionization signatures are equally strong for models with different non-adiabatic shock electron heating efficiencies. We have also calculated the detectability of the O VII and O VIII lines with the future International X-ray Observatory (IXO). Depending on the line ratio measured, we conclude that an exposure of ~130-380 ks on a moderate-redshift, massive regular cluster with the X-ray Microcalorimeter Spectrometer (XMS) on the IXO will be sufficient to provide a strong test for the non-equilibrium ionization model.
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|a United States. National Aeronautics and Space Administration (Grant GO7-8129X)
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|a United States. National Aeronautics and Space Administration (Grant GO7-8081A)
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|a United States. National Aeronautics and Space Administration (Grant GO8-9083X)
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|a United States. National Aeronautics and Space Administration (Grant GO9-0135X)
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|a United States. National Aeronautics and Space Administration (Grant GO9-0148X)
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|a United States. National Aeronautics and Space Administration (Grant NNX08AZ34G)
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|a United States. National Aeronautics and Space Administration (Grant NNX09AH25G)
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|a United States. National Aeronautics and Space Administration (Grant NNX08AW83G)
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|a United States. National Aeronautics and Space Administration (Grant NNX08Z99G)
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|a United States. National Aeronautics and Space Administration (Grant NNX09AH74G)
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|a en_US
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|a Article
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|t Astrophysical Journal
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