The Cluster HEritage project with XMM-Newton – Mass Assembly and Thermodynamics at the Endpoint of structure formation (CHEX-MATE) is a three-mega-second Multi-Year Heritage Programme to obtain X-ray observations of a minimally-biased, signal-to-noise-limited sample of 118 galaxy clusters detected by Planck through the Sunyaev–Zeldovich effect. The programme aims to study the ultimate products of structure formation in time and mass. It is composed of a census of the most recent objects to have formed (Tier-1: 0.05 < z < 0.2; 2 × 10¹⁴ M_⊙ < M₅₀₀ < 9 × 10¹⁴ M_⊙), together with a sample of the highest mass objects in the Universe (Tier-2: z < 0.6; M₅₀₀ > 7.25 × 10¹⁴ M_⊙). The programme will yield an accurate vision of the statistical properties of the underlying population, measure how the gas properties are shaped by collapse into the dark matter halo, uncover the provenance of non-gravitational heating, and resolve the major uncertainties in mass determination that limit the use of clusters for cosmological parameter estimation.

A key aspect of the programme is acquisition of X-ray exposures of uniform depth, designed to obtain individual mass measurements accurate to 15−20% under the hydrostatic assumption. A significant (and exceptional) multi- wavelength observational and simulation effort is also being deployed as part of the project. To this end, full and homogeneous coverage is being obtained in multi-band optical imaging, optical spectroscopy, millimetre, and radio wavelengths.

The Steering Committee Team Meeting in ISSI, Bern allows the SC to plan the exploitation of this unique multi-wavelength data set.