Unconventional ways to measure the Hubble constant with lensed and non-lensed supernovae

Abstract:

The precise determination of the Hubble constant has gained enormous attention after a discrepancy between local and early-universe measurements has become evident with the release of the first data from the Planck satellite almost 10 years ago.

Since then, this discrepancy, known as the "Hubble tension", has grown to more than 5 sigma, and may hint at new physics beyond the LambdaCDM standard model of cosmology. I will present two projects that aim to use supernovae to measure the Hubble constant in the local universe. Both methods provide stand-alone one-step measurements that are completely independent of the distance ladder. In the first approach, the "adH0cc" collaboration augments the classical expanding-photosphere method with tailored spectral modelling to determine distances of Type II supernovae.

The method is applied to spectral time series of supernovae in the Hubble flow obtained through a dedicated ESO Large Programme. In the second approach, the "HOLISMOKES" team aims to use supernovae that are strongly lensed and multiply imaged by a massive foreground galaxy. By measuring the temporal delays between their multiple images, the so-called time-delay distance and hence the Hubble constant can be inferred. From both programmes we expect measurements with 5% precision within the next years.