SMuK 2023 – scientific programme
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EP: Fachverband Extraterrestrische Physik
EP 15: Astrophysics: Cosmology
EP 15.2: Talk
Friday, March 24, 2023, 14:15–14:30, HSZ/0004
Determining H0 without a distance ladder — •Hanna Belgardt and Dieter Horns — Institut für Experimentalphysik, Universität Hamburg, Luruper Chausseee 149, D-22761 Hamburg
The Hubble constant H0 gives the present expansion rate of the universe. The value of H0 is commonly determined using the cosmic distance ladder. Here, we present a method to measure H0 via the distance-dependent attenuation of very-high energy (VHE) gamma-ray photons propagating in the extra-galactic background light (EBL).
We use a sample of VHE photon spectra of extragalactic sources including active galactic nuclei and gamma-ray bursts. We fit spectral models, which include the attenuation due to the pair production with the EBL photons. This attenuation can be characterized by an optical depth τ(H0). We perform a fitting procedure to minimise the χ2 and hence obtain an estimator for the Hubble constant.
Using the Domínguez et al. (2010) EBL model our preliminary analysis yields a best fit value of H0 = 76 ± 6 km/s/Mpc. This result is close and competitive to the value found with the cosmic distance ladder technique, e.g., H0=73(+2.6 / −2.3)km/s/Mpc (Kenworthy et al. 2022.) Final results will be shown at the conference.