Cosmology from eROSITA’s X-ray Observations

Abstract: We review the cosmological results derived from the X-ray observations of the eROSITA mission. While some studies used the auto- and cross-correlation function of X-ray map itself, we will highlight how to find and characterize galaxy clusters by combining eROSITAs X-ray observation with optical photometric surveys. As galaxy clusters inhabitmassive halos, the resulting eROSITA cluster sample can be  used to constrain cosmology via the halo mass function. We present weak gravitational lensing measurements of the eROSITA clusters, used to calibrate their mass scale. The joint fit of the mass calibration, the halo mass function and the selection function is performed with a Bayesian Population model, whose structure and astrophysical assumption we discuss. The resulting posterior distribution is presented, with a focus on the inferred cosmological parameters. WL calibrated cluster number count result as a competitive cosmological probe of the Large Scale Structure, Dark Energy, the summed neutrino mass and modified Gravity. We conclude in highlighting the potential of cluster cosmology to constrain the baryon distribution in the Universe, with a brief outlook on future surveys and lines of inquiry.