Orateur
Description
The Legacy Survey of Space and Time (LSST) has now started its ten-year survey. Its promise: detecting of order 100,000 galaxy clusters up to z~1, while providing weak-lensing information for a substantial fraction of them. The weak-lensing measurements will allow us to calibrate the relation between cluster observables, such as richness and halo mass. Combined with complementary Stage IV surveys, these data will offer an unprecedented opportunities for cosmological analyses.
The abundance of galaxy clusters as a function of mass and redshift is a powerful probe of the growth of cosmic structure and expansion history of the Universe, being sensitive to parameters such as OmegaM, sigma8.
As statistical power increases, the accuracy of the cosmological inference increasingly depends on our control of selection effects, calibration uncertainties, astrophysical and theoretical modeling, and statistical methodology.
The current challenge is therefore shifting from an era where the need was to obtain more objects to an era where the need is to establish that the mapping from observables to cosmological parameters is unbiased. In this context, could an apparently significant deviation from ΛCDM or at the contrary an apparently good agreement between ΛCDM and our data, be an artifact of a biased mapping ?
Using the example of galaxy clusters, this talk will review the analysis steps that go from imaging to cosmological inference, focusing on the various assumptions, approximations and potential circularities and hidden dependencies that enter the analysis and may bias the final result. Ideas on how to make the measurement more robust will then be discussed.