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Register a new userThe Galaxy Cluster RBS380: Xray and Optical Analysis
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R. Gil-Merino
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We present X-ray and optical observations of the z=0.52 galaxy cluster RBS380. This is the most distant cluster in the ROSAT Bright Source catalog. The cluster was observed with the CHANDRA satellite in September 2000. The optical observations were carried out with the NTT-SUSI2 camara in filters V and R in August and September 2001. The preliminary conclusions are that we see a very rich optical galaxy cluster but with a relative low X-ray luminosity. We also compare our results to other clusters with similar properties.
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We use imaging from the first three years of the Dark Energy Survey to characterize the dynamical state of 288 galaxy clusters at $0.1 lesssim z lesssim 0.9$ detected in the South Pole Telescope (SPT) Sunyaev-Zeldovich (SZ) effect survey (SPT-SZ). We examine spatial offsets between the position of the brightest cluster galaxy (BCG) and the center of the gas distribution as traced by the SPT-SZ centroid and by the X-ray centroid/peak position from Chandra and XMM data. We show that the radial distribution of offsets provides no evidence that SPT SZ-selected cluster samples include a higher fraction of mergers than X-ray-selected cluster samples. We use the offsets to classify the dynamical state of the clusters, selecting the 43 most disturbed clusters, with half of those at $z gtrsim 0.5$, a region seldom explored previously. We find that Schechter function fits to the galaxy population in disturbed clusters and relaxed clusters differ at $z>0.55$ but not at lower redshifts. Disturbed clusters at $z>0.55$ have steeper faint-end slopes and brighter characteristic magnitudes. Within the same redshift range, we find that the BCGs in relaxed clusters tend to be brighter than the BCGs in disturbed samples, while in agreement in the lower redshift bin. Possible explanations includes a higher merger rate, and a more efficient dynamical friction at high redshift. The red-sequence population is less affected by the cluster dynamical state than the general galaxy population.
We present CHANDRA X-ray and NTT optical observations of the distant z=0.52 galaxy cluster RBS380 -- the most distant cluster of the ROSAT Bright Source (RBS) catalogue. We find diffuse, non-spherically symmetric X-ray emission with a X-ray luminosity of L_X(0.3-10 keV)=1.6 10^(44) erg/s, which is lower than expected from the RBS. The reason is a bright AGN in the centre of the cluster contributing considerably to the X-ray flux. This AGN could not be resolved with ROSAT. In optical wavelength we identify several galaxies belonging to the cluster. The galaxy density is at least 2 times higher than expected for such a X-ray faint cluster, which is another confirmation of the weak correlation between X-ray luminosity and optical richness. The example of the source confusion in this cluster shows how important high-resolution X-ray imaging is for cosmological research.
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