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Batch discovery of nine z∼ 1 clusters using X-ray and K or R, z' images
Authors:S Andreon  I Valtchanov  L R Jones  B Altieri  M Bremer  J Willis  M Pierre  H Quintana
Institution:INAF-Osservatorio Astronomico di Brera, Milano, Italy;Astrophysics group, Blackett Laboratory, Imperial College, London;School of Physics and Astronomy, University of Birmingham, Birmingham;XMM-Newton Science Operations Centre, European Space Agency, Villafranca del Castillo, Spain;Department of Physics, Bristol University, Bristol;Department of Physics and Astronomy, University of Victoria, Victoria, Canada;CEA/DSM/DAPNIA, Service d'Astrophysique, Gif -sur-Yvette, France;Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Santiago, Chile
Abstract:We present the results of an initial search for clusters of galaxies at z ~ 1 and above, using data from 2.9 square degrees of XMM–Newton images. By selecting weak potentially extended X-ray sources with faint or no identifications in deep, ground-based optical imaging, we have constructed a starting sample of 19 high-redshift cluster candidates. Near-IR and R , z ' imaging of these fields identified nine of them as high-redshift systems. Six of these were confirmed spectroscopically, three at z ~ 1.0 and the other three in the  0.8 < z < 0.92  range. The remaining three systems have solid photometric evidence to be at   z phot~ 0.8, 1.0  and 1.3. The present sample significantly increases the number of such clusters. The measured density of z ? 1 clusters, after discarding 'low'-redshift systems at z ? 0.92 is about 1.7 deg?2 (with 68 per cent confidence interval equal to 1.0, 2.9]) for   fX ? 2.5  10?15 erg cm?2 s?1  (0.5–2] keV) and this is a lower limit, having screened not all potential z ~ 1 candidate clusters. Coordinates, X-ray measures and evidence for nine X-ray-selected high-redshift clusters is given.
Keywords:galaxies: clusters: general  cosmology: observations  X-rays: galaxies: clusters
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