Journal Article

A blind detection of a large, complex, Sunyaev–Zel’dovich structure*

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

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 2, pages 1463-1473
Published in print June 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI:
A blind detection of a large, complex, Sunyaev–Zel’dovich structure*

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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.

Keywords: galaxies: clusters: general; cosmology: observations

Journal Article.  7190 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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