2012MNRAS.423.1463A

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 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 {x} 10⁴:1; alternatively assuming [Jenkins et al.] as the true prior, the formal Bayesian probability ratio of detection is 2.1 {x} 10⁵:1. (b) The cluster mass is M_T.200 = = 5.5 ^+1.2_–1.3 x 10^14h-1^₇₀M_☉. (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 -295⁺³⁶_–15µK – 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.

We request that any reference to this paper cites `AMI Consortium: Shimwell et al. 2012'.