No rungs attached: A distance-ladder-free determination of the Hubble constant through type II supernova spectral modelling

¹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
² Technische Universität München, TUM School of Natural Sciences, Physics Department, James-Franck-Straße 1, 85748 Garching, Germany
³ Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany
⁴ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
⁵ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁶ Exzellenzcluster ORIGINS, Boltzmannstr. 2, 85748 Garching, Germany
⁷ Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
⁸ Department of Computational Mathematics, Science, and Engineering, Michigan State University, East Lansing, MI 48824, USA
⁹ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
¹⁰ GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße 1, 64291 Darmstadt, Germany
¹¹ Department of Physics, Duke University, Durham, NC 27708, USA
¹² University Claude Bernard Lyon 1, IUF, IP2I Lyon, 69622 Villeurbanne, France

^⋆ Corresponding author: cvogl@mpa-garching.mpg.de

Received: 6 November 2024
Accepted: 19 May 2025

Abstract

Context. The ongoing discrepancy among Hubble constant (H₀) estimates obtained through local distance ladder methods and early Universe observations poses a significant challenge to the ΛCDM model, suggesting potential new physics. Type II supernovae (SNe II) offer a promising technique for determining H₀ in the Local Universe independently of the traditional distance ladder approach, opening up a complimentary path for testing this discrepancy.

Aims. We aim to provide the first H₀ estimate using the tailored expanding photosphere method (EPM) applied to SNe II, made possible by recent advancements in spectral modelling that enhance its precision and efficiency.

Methods. Our tailored EPM measurement utilises a spectral emulator to interpolate between radiative transfer models calculated with TARDIS, allowing us to fit SN spectra efficiently and derive self-consistent values for luminosity-related parameters. We applied the method to a set of public data for ten SNe II at redshifts between 0.01 and 0.04.

Results. Our analysis demonstrates that the tailored EPM allows us to obtain H₀ measurements with a precision comparable to the most competitive established techniques, even when applied to literature data that are not designed for cosmological applications. We find an independent H₀ value of 74.9 ± 1.9 (stat) km s⁻¹ Mpc⁻¹, which is consistent with most current local measurements. Considering dominant sources of systematic effects, we conclude that our systematic uncertainty is comparable to (or less than) the current statistical uncertainty.

Conclusions. This proof-of-principle study highlights the potential of the tailored EPM as a robust and precise tool for investigating the Hubble tension independently of the local distance ladder. Observations of SNe II tailored to H₀ estimations could make this an even more powerful tool by improving the precision and allowing us to improve our understanding of the systematic uncertainties and how to control them.