Planck intermediate results. VIII. Filaments between interacting clusters
Böhringer, H.; Kneissl, R.; Bernard, J. -P.; Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Benabed, K.; Benoît, A.; Bersanelli, M.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Burigana, C.; Cardoso, J. -F.; Catalano, A.; Chamballu, A.; Chary, R. -R.; Christensen, P. R.; Clements, D. L.; Colombo, L. P. L.; Coulais, A.; Crill, B. P.; Cuttaia, F.; Danese, L.; Davis, R. J.; de Bernardis, P.; de Zotti, G.; Delabrouille, J.; Désert, F. -X.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Ganga, K.; Giard, M.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Gruppuso, A.; Hansen, F. K.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hovest, W.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Kisner, T. S.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J. -M.; Lasenby, A.; Lawrence, C. R.; Le Jeune, M.; Leonardi, R.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maino, D.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martínez-González, E.; Masi, S.; Matarrese, S.; Melchiorri, A.; Mendes, L.; Mennella, A.; Mitra, S.; Moneti, A.; Montier, L.; Morgante, G.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Pajot, F.; Paoletti, D.; 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.; Prunet, S.; Puget, J. -L.; Rachen, J. P.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Savini, G.; Scott, D.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A. -S.; Sygnet, J. -F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Valenziano, L.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Yvon, D.; Zacchei, A.; Zonca, A.; White, S. D. M.; Popa, L.; Van Tent, B.; Massardi, M.; Bikmaev, I.; Starck, J. -L.; Colafrancesco, S.; Bourdin, H.; Mazzotta, P.; Maffei, B.; Knox, L.; Welikala, N.; Mei, S.; Ponthieu, N.; Atrio-Barandela, F.; Chiang, L. -Y.; Harrison, D.; Matthai, F.; Osborne, S.; Poutanen, T.; Ricciardi, S.; Riller, T.; Vittorio, N.; Comis, B.; Chon, G.; Burenin, R.; Balbi, A.; Bhatia, R.; Cabella, P.; Cayón, L.; de Gasperis, G.; Dörl, U.; Smoot, G. F.; Hempel, A.; Luzzi, G.; Melin, J. -B.; Roman, M.; Castex, G.; Démoclès, J.; Dolag, K.; Flores-Cacho, I.; Frommert, M.; Jagemann, T.; Khamitov, I.; Marleau, F.; Piffaretti, R.; Gilfanov, M.; Schaefer, B. M.; Miville-Deschènes, M. -A.; Battaner, J. G. Bartlett E.; Génova-Santos, T.
Abstract
Context. About half of the baryons of the Universe are expected to be in the form of filaments of hot and low-density intergalactic medium. Most of these baryons remain undetected even by the most advanced X-ray observatories, which are limited in sensitivity to the diffuse low-density medium.
Aims: The Planck satellite has provided hundreds of detections of the hot gas in clusters of galaxies via the thermal Sunyaev-Zel'dovich (tSZ) effect and is an ideal instrument for studying extended low-density media through the tSZ effect. In this paper we use the Planck data to search for signatures of a fraction of these missing baryons between pairs of galaxy clusters.
Methods: Cluster pairs are good candidates for searching for the hotter and denser phase of the intergalactic medium (which is more easily observed through the SZ effect). Using an X-ray catalogue of clusters and the Planck data, we selected physical pairs of clusters as candidates. Using the Planck data, we constructed a local map of the tSZ effect centred on each pair of galaxy clusters. ROSAT data were used to construct X-ray maps of these pairs. After modelling and subtracting the tSZ effect and X-ray emission for each cluster in the pair, we studied the residuals on both the SZ and X-ray maps.
Results: For the merging cluster pair A399-A401 we observe a significant tSZ effect signal in the intercluster region beyond the virial radii of the clusters. A joint X-ray SZ analysis allows us to constrain the temperature and density of this intercluster medium. We obtain a temperature of kT = 7.1 ± 0.9 keV (consistent with previous estimates) and a baryon density of (3.7 ± 0.2) × 10-4 cm-3.
Conclusions: The Planck satellite mission has provided the first SZ detection of the hot and diffuse intercluster gas.