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The origin of X-ray emission of two distant (z>1) cluster candidate with XMM-Newton

D. M. Neumann·M. Arnaud·C. Benoist·L. da Costa·H. E. Jørgensen·L. F. Olsen·S. Bardelli·E. Zucca·S. Arnouts·A. Biviano·M. Ramella
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Abstract

We present here a study of XMM-Newton data of two distant galaxy cluster candidates. One of these was discovered serendipitously in near infrared data, CL J0533-2411, the other one corresponds to the cluster EIS J0533-2412 part of the EIS cluster survey. The estimated redshift of CL J0533-2411 is z=1.2-1.7. EIS J0533-2412 is a rich system (Lambda_cl=299), with a spectroscopically confirmed redshift of z=1.3. Both galaxy concentrations show firm X-ray detections, located within 30" of their optical center. However, we cannot resolve the sources with XMM-Newton. If the X-ray emission originates from the X-ray emitting intra-cluster medium (ICM) it would be extremely concentrated which is rather unlikely (core radii below 14 h_{65}^{-1}kpc and 40 h_{65}^{-1}kpc, respectively). We argue that the X-ray sources are more likely AGN members of the galaxy concentrations. We set an upper limit for the bolometric luminosity of a hot ICM in the range ~0.7-2.1 10^{44} h_{65}^{-2}erg/s for CL J0533-2411, depending on the exact redshift. For EIS J0533-2412 the limit is L_bol=(6.2+/-1.4) 10^{43} h_{65}^{-2}erg/s. We interpret our result in the following way: EIS J0533-2412 (and possibly CL J0533-2411) are proto-clusters and show matter overdensities before collapse, which explains the low significance of extended X-ray emission.

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D. M. Neumann, M. Arnaud, C. Benoist, L. da Costa, H. E. Jørgensen, L. F. Olsen, S. Bardelli, E. Zucca, S. Arnouts, A. Biviano, M. Ramella. 2003-04-23. The origin of X-ray emission of two distant (z>1) cluster candidate with XMM-Newton. https://doi.org/10.1051/0004-6361%3A20030657

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