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

Michael Brown, AMI Consortium, 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 FelvusF Feroz, W Flynn, T M O Franzen, J Geisb??sch, R G??nova-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 Rodr??guez-Gonz??lvez, R D E Saunders, A M M Scaife, M P Schammel, J Schofield, P F Scott, C Shaw, H Smith, D J Titterington, M Veli??, E M Waldram, S West, B A Wood, G Yassin, J T L Zwart

    Research output: Contribution to journalArticlepeer-review


    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 (≈10arcmin) 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 × 10 4:1; alternatively assuming Jenkins et al. as the true prior, the formal Bayesian probability ratio of detection is 2.1 × 10 5:1. (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. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.
    Original languageEnglish
    Pages (from-to)1463-1473
    Number of pages11
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number2
    Publication statusPublished - Jun 2012


    • Cosmology: observations
    • Galaxies: clusters: general


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