Speaker: Radoslaw Wojtak (Niels Bohr institute)
Title: Is the Hubble constant tension a cosmological anomaly?
Abstract: The Hubble constant tension is a discrepancy between the Hubble constant values inferred from the cosmic microwave background radiation (Planck) and the cosmic distance ladder based on observations of Cepheids and type Ia supernovae (SH0ES). The tension cannot be fully resolved by any of the currently known modifications to the standard LCDM cosmological model. In my talk, I will discuss observational arguments, based on my recent reanalyses of the Cepheid and type Ia supernova data from the SH0ES project, that the Hubble constant tension may likely result from unaccounted for systematic errors related to modelling colour-dependent corrections of supernova peak magnitudes used as distance indicators. I will show that the current observations point to a stronger extinction correction of supernovae in the calibration galaxies (late-type galaxies selected for Cepheid observations) than in the Hubble flow. Accounting for this apparent difference between the calibration sample and the Hubble flow results in a significant reduction of the Hubble constant tension. I will discus these results in a broader context of models used to standardise type Ia supernovae in relation to their intrinsic and environment-dependent properties. I will show preliminary results from new two-population hierarchical Bayesian modelling of type Ia supernovae which has the potential to shed more light onto these problems.