The M2C project aims to test the theoretical underpinnings of the Lambda Cold Dark Matter model using the evolution of the dark matter profiles in the most massive galaxy clusters in the Universe. The project builds on the advent of cluster detection via the SZ effect, the sensitivity of current X-ray observatories, and recent advances in numerical simulations.
In the course of the project we aim to assemble a catalogue of virtually all massive (M > 5 x 1014 M?) galaxy clusters back to z~1. We build on the Planck SZ survey, the first All Sky survey since the ROSAT X-ray Survey (RASS). We will substantially extend the legacy Planck cluster catalogue by developing novel detection techniques based on a simultaneous search of objects in Planck and RASS maps, reaching lower masses at high redshifts, while keeping a high catalogue purity. Extension of the method to Planck/eROSITA will be studied in parallel.
For the first time, we will have the sample size, redshift leverage, and completeness, for a decisive test of the standard LCDM model of the dark matter gravitational collapse on cluster scales. The test will be provided by a full statistical analysis of the dark matter profiles and their evolution. The X-ray technique to derive mass profiles will be extended to the full cluster population. This will be made possible by an integrated approach involving systematic confrontation of observations with tailor-made numerical simulations, allowing us to disentangle observational biases from genuine departures from the standard scenario. We will also make use of our in-house X-ray satellite simulator on a case-by-case basis. Additional leverage will be provided by lensing data, in collaboration with external groups.
A major secondary goal of the M2C is to assess the dynamical behaviour and evolution of the baryons as they collect in the dark matter potential. Using multi-wavelength data of the largest, well-controlled sample of the most massive systems in the Universe, and simulations, we will
- provide the first complete census of the dark matter, hot and cold baryons and their evolution
- quantify the thermo- dynamical state up to z~1 as a probe of hierarchical structure formation and gravitational heating
- probe the link between non-thermal and thermal components.
Ultimately, the project will either cement our current understanding of the dark matter collapse, a prerequisite to any assessment of the specific baryon physics, or point towards the need for revision of the current paradigm, with important cosmological implications. The new detection techniques will be applicable to future surveys, some of which, such as eROSITA, will come online during the course of the project. Lastly, we will provide a ‘gold sample’ of galaxy clusters, ideal for cosmological parameter estimates.
