An XMM-Newton observation of the dynamically active binary cluster A1750

We present results from the XMM-Newton observation of the binary cluster A1750 at $z = 0.086$. We have performed a detailed study of the surface brightness, temperature and entropy distribution and confirm that the two main clusters of the system (A1750 N and A1750 C) have just started to interact. From the temperature distribution, we calculate that they are likely to merge sometime in the next 1 Gyr. The more massive cluster, A1750 C, displays a more complicated temperature structure than expected. We detect a hot region associated with a density jump ~450 kpc east of the cluster centre, which appears to be a shock wave. This shock is not connected with the binary merger, but it is intrinsic to A1750 C itself. From simple physical arguments and comparison with numerical simulations, we argue that this shock is related to a merging event that A1750 C has suffered in the past 1-2 Gyr. The larger scale structure around A1750 suggests that the system belongs to a rich supercluster, which would presumably increase the likelihood of merger events. These new XMM-Newton data thus show that A1750 is a complex system, where two clusters are starting to interact before having re-established equilibrium after a previous merger. This merger within a merger indicates that the present day morphology of clusters may depend not only on on-going interactions or the last major merging event, but also on the more ancient merger history, especially in dense environments.