The Three Hundred Project: Validating

Measurements of thermodynamical quantities in galaxy clusters are differently affected by simplified modelling of radially averaged observables in the X-ray and millimetre bands. This includes assumptions about the cosmological model and the morphology of the cluster intracluster medium (ICM). Within a large sample of clusters extracted from THE THREE HUNDRED hydrodynamical simulations, we assess the systematic differences expected from the morphological assumptions between ICM temperatures as inferred from X-ray spectroscopy or joint X-ray and millimetre imaging. We find that these differences show a well-defined statistical behaviour that correlates with the cluster dynamical and morphological indicators. We then investigate how joint inferences of cluster temperature profiles, a priori informed by this statistical behaviour, allow us to constrain cosmological parameters inferred from the apparent cluster sizes. Assuming a flat Λ cold dark matter (ΛCDM) cosmology and priors on Ωm and the helium abundance, this method provides us with unbiased estimates of the Hubble constant, H0, characterised with a precision of about 4% and 1.5% for samples of 100 and 1000 clusters, respectively, and ultimately limited by systematic uncertainties of about 0.6–0.8 km s−1 Mpc−1. This work highlights the potential of joint X-ray and millimetre observations of galaxy cluster samples to place tight constraints on H0.