A blind detection of a large, complex, Sunyaev-Zel'dovich structure

AMI Consortium; Shimwell, T. W.; Barker, R. W.; Biddulph, P.; Bly, D.; Boysen, R. C.; Brown, A. R.; Brown, M. L.; Clementson, C.; Crofts, M.; Culverhouse, T. L.; Czeres, J.; Dace, R. J.; Davies, M. L.; D'Alessandro, R.; Doherty, P.; Duggan, K.; Ely, J. A.; Felvus, M.; Feroz, F.; Flynn, W.; Franzen, T. M. O.; Geisbüsch, J.; Génova-Santos, R.; Grainge, K. J. B.; Grainger, W. F.; Hammett, D.; Hobson, M. P.; Holler, C. M.; Hurley-Walker, N.; Jilley, R.; Kaneko, T.; Kneissl, R.; Lancaster, K.; Lasenby, A. N.; Marshall, P. J.; Newton, F.; Norris, O.; Northrop, I.; Odell, D. M.; Olamaie, M.; Perrott, Y. C.; Pober, J. C.; Pooley, G. G.; Pospieszalski, M. W.; Quy, V.; Rodríguez-Gonzálvez, C.; Saunders, R. D. E.; Scaife, A. M. M.; Schammel, M. P.; Schofield, J.; Scott, P. F.; Shaw, C.; Smith, H.; Titterington, D. J.; Velić, M.; Waldram, E. M.; West, S.; Wood, B. A.; Yassin, G.; Zwart, J. T. L.
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Monthly Notices of the Royal Astronomical Society, Volume 423, Issue 2, pp. 1463-1473.

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We present an interesting Sunyaev-Zel’dovich (SZ) detection in the first of the Arcminute Microkelvin Imager (AMI) ‘blind’, degree-square fields to have been observed down to our target sensitivity of ?. In follow-up deep pointed observations the SZ effect is detected with a maximum peak decrement greater than eight times the thermal noise. No corresponding emission is visible in the ROSAT all-sky X-ray survey and no cluster is evident in the Palomar all-sky optical survey. Compared with existing SZ images of distant clusters, the extent is large (≈10 arcmin) and complex; our analysis favours a model containing two clusters rather than a single cluster. Our Bayesian analysis is currently limited to modelling each cluster with an ellipsoidal or spherical β model, which does not do justice to this decrement. Fitting an ellipsoid to the deeper candidate we find the following. (a) Assuming that the Evrard et al. approximation to Press & Schechter correctly gives the number density of clusters as a function of mass and redshift, then, in the search area, the formal Bayesian probability ratio of the AMI detection of this cluster is 7.9 × 104:1; alternatively assuming Jenkins et al. as the true prior, the formal Bayesian probability ratio of detection is 2.1 × 105:1. (b) The cluster mass is ?. (c) Abandoning a physical model with number density prior and instead simply modelling the SZ decrement using a phenomenological β model of temperature decrement as a function of angular distance, we find a central SZ temperature decrement of ?K - this allows for cosmic microwave background primary anisotropies, receiver noise and radio sources. We are unsure if the cluster system we observe is a merging system or two separate clusters. We request that any reference to this paper cites ‘AMI Consortium: Shimwell et al. 2012’.
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