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

• Published in: arXiv.org 2012-03
• Main Authors: Consortium, AMI, 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, Geisbusch, J, Genova-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, Y C Perrott J C Pober, Pooley, G G, Pospieszalski, M W, Quy, V, Rodriguez-Gonzalvez, C, Saunders, R D E, Scaife, A M M, Schammel, M P, Schofield, J, Scott, P F, Shaw, C, Smith, H, Titterington, D J, Velic, M, Waldram, E M, West, S, Wood, B A, Yassin, G, Zwart, J T L
• Format: Article
• Language: English
• Subjects: Bayesian analysis; Clusters; Density; Elliptic fitting; Modelling; Red shift; Sky surveys (astronomy); Thermal noise
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1012.4441

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 100{\mu}Jy/beam. In follow-up deep pointed observations the SZ effect is detected with a maximum peak decrement greater than 8 \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 (\approx 10') 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 beta-model, which do not do justice to this decrement. Fitting an ellipsoid to the deeper candidate we find the following. (a) Assuming that the Evrard et al. (2002) approximation to Press & Schechter (1974) 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 \times 10^4:1; alternatively assuming Jenkins et al. (2001) as the true prior, the formal Bayesian probability ratio of detection is 2.1 \times 10^5:1. (b) The cluster mass is MT,200 = 5.5+1.2\times 10^14h-1M\odot. (c) Abandoning a physical model with num- -1.3 70 ber density prior and instead simply modelling the SZ decrement using a phenomenological {\beta}-model of temperature decrement as a function of angular distance, we find a central SZ temperature decrement of -295+36 {\mu}K - this allows for CMB primary anisotropies, receiver -15 noise and radio sources. We are unsure if the cluster system we observe is a merging system or two separate clusters.