1. A blind detection of a large, complex, Sunyaev--Zel'dovich structure
- Author
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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., Pober, Y. C. Perrott J. C., 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., and Zwart, J. T. L.
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Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
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., Comment: accepted MNRAS. 12 pages, 9 figures
- Published
- 2010
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