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M. Galeazzi, E. Ursino (University of Miami), W. T. Sanders (University of Wisconsin)
The number of detected baryons in the Universe at z<0.5 is much smaller than predicted by standard big bang nucleosynthesis and by the detailed observation of the Lyman alpha forest at red-shift z=2. Hydrodynamical simulations indicate that a large fraction of the baryons today is expected to be in a ''warm-hot'' (105~V 107 K) filamentary gas, distributed in the intergalactic medium (WHIM). It is currently believed that a significant fraction of the diffuse x-ray background in the energy band 0.5-1 keV is due to thermal emission from this intergalactic medium. The signature of the WHIM can be observed in red-shifted (z < 1) strong soft x-ray and UV emission lines from highly ionized elements.
Using the prediction of the hydrodynamic models we simulated the expected x-ray emission due to the WHIM and compared it with local and high red-shift components. We then investigated the effect of the X-ray emission due to the WHIM on future missions as Astro-E2 and Constellation-X.
Our results show that as much as 20% of the diffuse x-ray background (DXB) in the energy range 0.37-0.925 keV could be due to x-ray emission from the WHIM, 70% of which comes from gas at red-shift z between 0.1 and 0.6. Simulations done using a FOV of 3~R, comparable with that of Astro-E2 and Constellation-X, also show that in more than 40% of the observations we expect the WHIM emission to contribute to more than 20% of the DXB. These simulations also show that in more than 20% of all the observations the WHIM emission is due to a single bright filament in the FOV that accounts, alone, for more than 20% of the DXB emission. Red-shifted oxygen lines should be clearly visible in these observations.
The author(s) of this abstract have provided an email address for comments about the abstract: galeazzi@physics.miami.edu
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.