ISDC Science Results
Probing the cosmic-ray content of galaxy clusters by stacking Fermi-LAT count maps
2013-10-02 | Fermi, VHE, Galaxy cluster
The cosmic-ray content of galaxy clusters is expected to produce a gamma-ray signal that could be detected by the Fermi Gamma-ray Space Telescope. We show here that even by stacking the Fermi observations at the position of 53 known galaxy clusters we still cannot detect such an emission.
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The baryon content of galaxy clusters in their entire volume
2013-01-07 | Galaxy cluster, Cosmology, Planck | Press Release
Galaxy clusters form from the largest inhomogeneities of the early Universe, and thus they are expected to retain their mass (both baryonic and dark matter) throughout cosmic time. We measure for the first time the baryon fraction of galaxy clusters in their entire volume by combining X-ray (ROSAT) and Sunyev-Zel'dovich (Planck) data. As expected, we find that the average baryon fraction reaches the cosmic value Ωb/Ωm in the outer regions, which shows that clusters are suitable targets for cosmological studies.
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Thermodynamic properties of the virial region of galaxy clusters
2013-01-07 | Galaxy cluster, Planck
Galaxy clusters are still forming in their outer regions through the accretion of smaller structures (galaxies, groups). Using a combined X-ray (ROSAT) and Sunyaev-Zel'dovich (Planck) data analysis, we determine the thermodynamic properties of a sample of 18 galaxy clusters and constrain the current mechanisms of structure formation. We find that in unrelaxed clusters non-thermal effects (cosmic rays, turbulence, magnetic fields) and/or gas clumping play an important role, while relaxed cool-core clusters follow closely the predictions of gravitational collapse.
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The gas distribution in galaxy cluster outer regions
2011-11-01 | Galaxy cluster
We analyze archival ROSAT observations for a sample of 31 galaxy clusters to study the spatial distribution of the gas out to the virial radius of these objects, and compare this with state-of-the-art numerical simulations. We find that the mean observed density profiles are flatter than predicted by numerical simulations including gravitational collapse only, which indicates that non-gravitational processes (gas cooling, clumping, AGN feedback) cannot be neglected even in regions with a very low density.
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