Physics
Scientific paper
Apr 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aps..apr.h8002m&link_type=abstract
American Physical Society, 2008 APS April Meeting and HEDP/HEDLA Meeting, April 11-15, 2008, abstract #H8.002
Physics
Scientific paper
Resent observations of a number of galaxy clusters using the Sunyaev-Zel'dovich effect indicate that about 1/3 of baryonic mass is missing from the hot intracluster medium (ICM), which is significantly larger than the fraction of stars and cool gas, which account for only about 10%. Here we address the question whether the remaining 22%±10% can be accounted for by thermal evaporation of gas from clusters. We have found that evaporation can occur only from the cluster ``surface'', r˜rvir, and not from it's interior. We evaluated particle diffusion through the magnetized ICM for several scenarios of ISM turbulence and found that diffusivity is suppressed by at least a factor of 100 or more, compared to the Spitzer value. Thus, only particles from radii r0.9rvir can evaporate. Diffusion of particles from inside the cluster, r0.9rvir, takes longer than the Hubble time. This lowers the cluster-averaged fraction of the evaporated hot gas to few percent or less. However, if the missing hot component is indeed due to evaporation, this strongly constrains the magnetic field structure in the cluster envelope, namely either (i) the gas is completely unmagnetized (B10-21 gauss) in the cluster halo or (ii) the magnetic fields in the ICM are rather homogeneous and non-turbulent.
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