Which galaxy clusters are recent mergers?

The Planck satellite has produced the first all-sky sample of galaxy clusters selected via the Sunyaev-Zel'dovich (SZ) effect. SZ has the advantage over the main existing way of finding clusters, that of X-ray imaging, because SZ is less biased to the concentration of gas produced by shocking during a merger. Recent mergers are expected to give enhanced values of (X-ray-measured temperature) / (SZ-measured-temperature). The Arcminute MIcrokelvin Imager (AMI) is an SZ telescope that measures SZ temperatures, and the project will use this to follow up on the large Planck cluster subset in the northern sky and get to grips with long-standing uncertainties about cluster merger statuses.