Planck early results. IX. XMM-Newton follow-up for validation of Planck cluster candidates

Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Balbi, A.; Banday, A. J.; Barreiro, R. B.; Bartelmann, M.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoit, A.; J. . . P.,; Bersanelli, M.; Bhatia, R.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Brown, M. L.; Bucher, M.; Burigana, C.; Cabella, P.; Cantalupo, C. M.; J. . . F.,; Carvalho, P.; Catalano, A.; Cayon, L.; Challinor, A.; Chamballu, A.; L. . . Y.,; Chon, G.; Christensen, P. R.; Churazov, E.; Clements, D. L.; Colafrancesco, S.; Colombi, S.; Couchot, F.; Coulais, A.; Crill, B. P.; Cuttaia, F.; Silva, A. D.; Dahle, H.; Danese, L.; Bernardis, P. d.; Gasperis, G. d.; Rosa, A. d.; Zotti, G. d.; Delabrouille, J.; J. . . M., F. . . X.; Diego, J. M.; Dolag, K.; Donzelli, S.; Dore, O.; Doerl, U.; Douspis, M.; Dupac, X.; Efstathiou, G.; Ensslin, T. A.; Finelli, F.; Flores Cacho, I.; Forni, O.; Frailis, M.; Franceschi, E.; Fromenteau, S.; Galeotta, S.; Ganga, K.; Genova Santos, R. T.; Giard, M.; Giardino, G.; Giraud Heraud, Y.; Gonzalez Nuevo, J.; Gonzalez Riestra, R.; Gorski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Harrison, D.; Heinamaki, P.; Henrot Versille, S.; Hernandez Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hovest, W.; Hoyland, R. J.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Juvela, M.; Keihanen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knox, L.; Kurki Suonio, H.; Lagache, G.; J. . . M.,; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Jeune, M. L.; Leach, S.; Leonardi, R.; Liddle, A.; Linden Vornle, M.; Lopez Caniego, M.; Lubin, P. M.; Macias Perez, J. F.; Maffei, B.; Maino, D.; Mandolesi, N.; Mann, R.; Maris, M.; Marleau, F.; Martinez Gonzalez, E.; Masi, S.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Melchiorri, A.; J. . . B.,; Mendes, L.; Mennella, A.; Mitra, S.; M. . . A.,; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, A.; Naselsky, P.; Natoli, Paolo; Netterfield, C. B.; Norgaard Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Osborne, S.; Pajot, F.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Piffaretti, R.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Poutanen, T.; Pratt, G. W.; Prezeau, G.; Prunet, S.; J. . . L.,; Rebolo, R.; Reinecke, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rubino Martin, J. A.; Rusholme, B.; Saar, E.; Sandri, M.; Santos, D.; Schaefer, B. M.; Scott, D.; Seiffert, M. D.; Smoot, G. F.; J. . . L.,; Stivoli, F.; Stolyarov, V.; Sunyaev, R.; J. . . F.,; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; J. . . P.,; Tristram, M.; Tuovinen, J.; Valenziano, L.; Vibert, L.; Vielva, P.; Villa, F.; Vittorio, N.; Wandelt, B. D.; S. D. M.,; Yvon, D.; Zacchei, A.; Zonca, A.

doi:10.1051/0004-6361/201116460

We present the XMM-Newton follow-up for confirmation of Planck cluster candidates. Twenty-five candidates have been observed to date using snapshot (similar to 10 ks) exposures, ten as part of a pilot programme to sample a low range of signal-to-noise ratios (4 < S/N < 6), and a further 15 in a programme to observe a sample of S/N > 5 candidates. The sensitivity and spatial resolution of XMM-Newton allows unambiguous discrimination between clusters and false candidates. The 4 false candidates have S/N <= 4.1. A total of 21 candidates are confirmed as extended X-ray sources. Seventeen are single clusters, the majority of which are found to have highly irregular and disturbed morphologies (about similar to 70%). The remaining four sources are multiple systems, including the unexpected discovery of a supercluster at z = 0.45. For 20 sources we are able to derive a redshift estimate from the X-ray Fe K line (albeit of variable quality). The new clusters span the redshift range 0.09 less than or similar to z less than or similar to 0.54, with a median redshift of z similar to 0.37. A first determination is made of their X-ray properties including the characteristic size, which is used to improve the estimate of the SZ Compton parameter, Y-500. The follow-up validation programme has helped to optimise the Planck candidate selection process. It has also provided a preview of the X-ray properties of these newly-discovered clusters, allowing comparison with their SZ properties, and to the X-ray and SZ properties of known clusters observed in the Planck survey. Our results suggest that Planck may have started to reveal a non-negligible population of massive dynamically perturbed objects that is under-represented in X-ray surveys. However, despite their particular properties, these new clusters appear to follow the Y-500-Y-X relation established for X-ray selected objects, where Y-X is the product of the gas mass and temperature.