A blind detection of a large, complex, Sunyaev--Zel'dovich structure
Creators: name: Consortium, AMI
name: :
name: Shimwell, T. W.
name: Barker, R. W.
name: Biddulph, P.
name: Bly, D.
name: Boysen, R. C.
name: Brown, A. R.
name: Brown, M. L.
name: Clementson, C.
name: Crofts, M.
name: Culverhouse, T. L.
name: Czeres, J.
name: Dace, R. J.
name: Davies, M. L.
name: D'Alessandro, R.
name: Doherty, P.
name: Duggan, K.
name: Ely, J. A.
name: Felvus, M.
name: Feroz, F.
name: Flynn, W.
name: Franzen, T. M. O.
name: Geisbusch, J.
name: Genova-Santos, R.
name: Grainge, K. J. B.
name: Grainger, W. F.
name: Hammett, D.
name: Hobson, M. P.
name: Holler, C. M.
name: Hurley-Walker, N.
name: Jilley, R.
name: Kaneko, T.
name: Kneissl, R.
name: Lancaster, K.
name: Lasenby, A. N.
name: Marshall, P. J.
name: Newton, F.
name: Norris, O.
name: Northrop, I.
name: Odell, D. M.
name: Olamaie, M.
name: Pober, Y. C. Perrott J. C.
name: Pooley, G. G.
name: Pospieszalski, M. W.
name: Quy, V.
name: Rodriguez-Gonzalvez, C.
name: Saunders, R. D. E.
name: Scaife, A. M. M.
name: Schammel, M. P.
name: Schofield, J.
name: Scott, P. F.
name: Shaw, C.
name: Smith, H.
name: Titterington, D. J.
name: Velic, M.
name: Waldram, E. M.
name: West, S.
name: Wood, B. A.
name: Yassin, G.
name: Zwart, J. T. L.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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 100μJy/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 &amp; 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 β-model of temperature decrement as a function of angular distance, we find a central SZ temperature decrement of -295+36 μK - 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.
description: accepted MNRAS. 12 pages, 9 figures