Context. The study of the thermodynamical and chemical properties of the intra cluster medium (ICM) in high redshift clusters of galaxies is a powerful tool for investigating the formation and evolution of large scale structures. Here we discuss the X-ray properties of clusters of galaxies optically selected in the red-sequence cluster survey (RCS) observed with the Chandra satellite, at redshifts 0.6 < z < 1.2. Aims. We intend to assess the evolutionary stage of optically selected high-z clusters of galaxies, performing a spectral analysis of the diffuse emission from their ICM. We also investigate the distribution of active galactic nuclei (AGN) in their surroundings. Methods. The background subtracted spectra were analyzed and fitted with a single temperature model to measure average ICM temperature, X-ray bolometric luminosity and Fe abundance within typical radii between 200 and 350 kpc. We also analyzed the point source number density and spatial distribution in the RCS clusters fields as a function of the X-ray flux. Results. We detected emission for the majority of the clusters, except for three, for which we have only marginal detection at similar to 3 sigma. We find that the normalization of the luminosity-temperature relation for RCS clusters is a factor of similar to 2 lower than the one for X-ray selected clusters. We confirm that the Fe abundance in the detected objects is consistent with that of X-ray selected clusters at the same redshift. We also find an excess of low-luminosity AGN towards the center of the clusters. Conclusions. At z similar to 1, optically selected clusters with a well-defined red-sequence show extended X-ray emission in about 70% (8/11) of the cases. Nevertheless, their L(X) - T(X) relation is significantly lower with respect to X-ray selected clusters at the same redshift, possibly indicating an incomplete virialization. The Fe abundance measured in the ICM of RCS clusters is comparable to the values measured for X-ray selected clusters at the same redshift, implying a substantial enrichment by SNe products. These two evidences add to the previously known studies of high-z, X-ray selected clusters, to confirm that the thermodynamical and chemical properties of the ICM are substantially established already at z > 1. Finally, we find the significant excess of medium and low luminosity AGN close to the centroid of the X-ray emission. Their X-ray emission is not dominating the ICM, but their presence may be relevant for studying the interaction between AGN and ICM.
Intra cluster medium properties and AGN distribution in high-z RCS clusters
ROSATI, Piero
2008
Abstract
Context. The study of the thermodynamical and chemical properties of the intra cluster medium (ICM) in high redshift clusters of galaxies is a powerful tool for investigating the formation and evolution of large scale structures. Here we discuss the X-ray properties of clusters of galaxies optically selected in the red-sequence cluster survey (RCS) observed with the Chandra satellite, at redshifts 0.6 < z < 1.2. Aims. We intend to assess the evolutionary stage of optically selected high-z clusters of galaxies, performing a spectral analysis of the diffuse emission from their ICM. We also investigate the distribution of active galactic nuclei (AGN) in their surroundings. Methods. The background subtracted spectra were analyzed and fitted with a single temperature model to measure average ICM temperature, X-ray bolometric luminosity and Fe abundance within typical radii between 200 and 350 kpc. We also analyzed the point source number density and spatial distribution in the RCS clusters fields as a function of the X-ray flux. Results. We detected emission for the majority of the clusters, except for three, for which we have only marginal detection at similar to 3 sigma. We find that the normalization of the luminosity-temperature relation for RCS clusters is a factor of similar to 2 lower than the one for X-ray selected clusters. We confirm that the Fe abundance in the detected objects is consistent with that of X-ray selected clusters at the same redshift. We also find an excess of low-luminosity AGN towards the center of the clusters. Conclusions. At z similar to 1, optically selected clusters with a well-defined red-sequence show extended X-ray emission in about 70% (8/11) of the cases. Nevertheless, their L(X) - T(X) relation is significantly lower with respect to X-ray selected clusters at the same redshift, possibly indicating an incomplete virialization. The Fe abundance measured in the ICM of RCS clusters is comparable to the values measured for X-ray selected clusters at the same redshift, implying a substantial enrichment by SNe products. These two evidences add to the previously known studies of high-z, X-ray selected clusters, to confirm that the thermodynamical and chemical properties of the ICM are substantially established already at z > 1. Finally, we find the significant excess of medium and low luminosity AGN close to the centroid of the X-ray emission. Their X-ray emission is not dominating the ICM, but their presence may be relevant for studying the interaction between AGN and ICM.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
