Planck early results. IX. XMM-Newton follow-up for validation of Planck cluster candidates
Kneissl, R.; Dahle, H.; Miville-Deschênes, M. -A.; Bernard, J. -P.; Planck Collaboration; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Bersanelli, M.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bucher, M.; Burigana, C.; Cardoso, J. -F.; Catalano, A.; Challinor, A.; Chamballu, A.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Couchot, F.; Coulais, A.; Crill, B. P.; Cuttaia, F.; Danese, L.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Désert, F. -X.; Diego, J. M.; Donzelli, S.; Doré, O.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Giard, M.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J. -M.; Lasenby, A.; Lawrence, C. R.; Le Jeune, M.; Leonardi, R.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maino, D.; Mandolesi, N.; Maris, M.; Martínez-González, E.; Masi, S.; Matarrese, S.; Melchiorri, A.; Mendes, L.; Mennella, A.; Mitra, S.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Naselsky, P.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Pajot, F.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J. -L.; Rebolo, R.; Reinecke, M.; Renault, C.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Scott, D.; Seiffert, M. D.; Stolyarov, V.; Sunyaev, R.; Sygnet, J. -F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tuovinen, J.; Valenziano, L.; Vielva, P.; Villa, F.; Wandelt, B. D.; Yvon, D.; Zacchei, A.; Zonca, A.; Churazov, E.; White, S. D. M.; Starck, J. -L.; Colafrancesco, S.; Mazzotta, P.; Maffei, B.; Knox, L.; Laureijs, R. J.; Ponthieu, N.; Giardino, G.; Bartelmann, M.; González-Riestra, R.; Chiang, L. -Y.; Delouis, J. -M.; Harrison, D.; Matthai, F.; Osborne, S.; Poutanen, T.; Ricciardi, S.; Riller, T.; Vittorio, N.; Chon, G.; Balbi, A.; Bhatia, R.; Cabella, P.; Cantalupo, C. M.; Cayón, L.; de Gasperis, G.; Dörl, U.; Hoyland, R. J.; Leach, S.; Mann, R.; Murphy, A.; Smoot, G. F.; Stivoli, F.; Torre, J. -P.; Génova-Santos, R. T.; Melin, J. -B.; Brown, M. L.; Carvalho, P.; Dolag, K.; Flores-Cacho, I.; Liddle, A.; Marleau, F.; Piffaretti, R.; Vibert, L.; Heinämäki, P.; Schaefer, B. M.; Fromenteau, S.; da Silva, A.; Saar, E.
Abstract
We present the XMM-Newton follow-up for confirmation of Planck cluster candidates. Twenty-five candidates have been observed to date using snapshot (~10ks) 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 ~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 ≲ z ≲ 0.54, with a median redshift of z ~ 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, Y500. 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 Y500-YX relation established for X-ray selected objects, where YX is the product of the gas mass and temperature.
Corresponding author: E. Pointecouteau, e-mail: etienne.pointecouteau@irap.omp.eu