Understand
We revisit the local Hubble constant measurement from type Ia supernovae calibrated with Cepheids (SH0ES) by remodelling the supernova data using two supernova populations emerging from the observed bimodal distribution of the SALT2 stretch parameter.
- Our analysis accounts for population differences in both intrinsic properties (related to possible initial conditions, including supernova progenitor channels) and host-galaxy extinction (expected from well-known environmental differences associated observationally with the two populations).
- Based on a two-population Bayesian hierarchical modelling of the SALT2 light-curve parameters from the Pantheon+ compilation, we simultaneously constrain intrinsic and extrinsic properties of both supernova populations, match probabilistically the calibration supernovae with the corresponding population in the Hubble flow, and derive the Hubble constant.
- The difference between the two supernova populations is primarily driven by their mean absolute magnitudes and total-to-selective extinction coefficients.