Witnessing the culmination of structure formation in the Universe

This is a Heritage program to study the ultimate products of structure formationin mass and time\\: a large, unbiased, signaltonoise limited sample of galaxyclusters detected by Planck via their SunyaevZeldovich effect. Completing thehighfidelity XMM coverage of this sample has extraordinary legacy value. Wewill (i) obtain an unbiased vision of the statistical properties of the clusterpopulation; (ii) uncover the provenance of nongravitational heating; (iii)measure how their gas is shaped by the collapse into dark matter haloes and themergers that built todays clusters; (iv) resolve the major uncertainties in massdeterminations that limit cosmological inferences; (v) build the foundation forcluster science with nextgeneration surveys. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]