Publications (2)0 Total impact
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Article: $XMM-Newton$ $\Omega$ project: III. Gas mass fraction shape in high redshift clusters
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ABSTRACT: We study the gas mass fraction, $f\_{\rm gas},$ behavior in $XMM-Newton$ $\Omega$ project. The typical $f\_{\rm gas}$ shape of high redshift galaxy clusters follows the global shape inferred at low redshift quite well. This result is consistent with the gravitational instability picture leading to self similar structures for both the dark and baryonic matter. However, the mean $f\_{\rm gas} in distant clusters shows some differences to local ones, indicating a departure from strict scaling. This result is consistent with the observed evolution in the luminosity-temperature relation. We quantitatively investigate this departure from scaling laws. Within the local sample we used, a moderate but clear variation of the amplitude of the gas mass fraction with temperature is found, a trend that weakens in the outer regions. These variations do not explain departure from scaling laws of our distant clusters. An important implication of our results is that the gas fraction evolution, a test of the cosmological parameters, can lead to biased values when applied at radii smaller than the virial radius. From our $XMM$ clusters, the apparent gas fraction at the virial radius is consistent with a non-evolving universal value in a high matter density model and not with a concordance.04/2005; -
Article: The environmental dependence of galaxy colors in intermediate redshift X-ray-selected clusters
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ABSTRACT: We present a wide-field imaging study of the colors of bright galaxies in 12 X-ray selected clusters and groups of galaxies at z ~ 0.3. The systems cover one of the largest ranges in X-ray luminosity (Lx ~ 10^43 - 10^45 erg/s), and hence mass, of any sample studied at this redshift. We find that the `red' galaxies form a tight color-magnitude relation (CMR) and that neither the slope nor zero-point of this relation changes significantly over the factor of 100 in X-ray luminosity of our sample. Using stellar population synthesis models we find our data allow a maximum possible change of 2 Gyrs in the typical age of the galaxies on the CMR over the range of Lx of our sample. We also measure the fraction of blue galaxies (fb) relative to the CMR in our clusters and find a low value of fb ~ 0.1 and find that there is no correlation between fb and Lx over our large Lx range. However, both the CMR and fb do depend on cluster radius, with the zero-point of the CMR shifting blueward in B-R by 0.10 +/- 0.036 magnitudes out to 0.75 times the virial radius, equivalent to a luminosity weighted age gradient of ~ 2.5 Gyrs per log(radius). It thus appears that the global cluster environment, in the form of cluster mass (Lx), has little influence on the properties of bright cluster galaxies, whereas the local environment, in the form of galaxy density (radius), has a strong effect. The range of ~ 100 in Lx corresponds to a factor of ~ 40 in ram-pressure efficiency, suggesting that ram-pressure stripping, or other mechanisms that depend on cluster mass like tidal stripping or harassment, are unlikely to be solely responsible for changing the galaxy population from the `blue' star forming galaxies, that dominate low density environments, to the `red' passive galaxies that dominate cluster cores.(abridged) Comment: 18 pages, 17 figures. Accepted for publication in ApJ03/2005;
