Sensitivity of the Hubble Constant Determination to Cepheid Calibration

TL;DR

This study re-evaluates the Cepheid calibration method for determining the Hubble constant, emphasizing individual galaxy extinction laws and color-luminosity relations, resulting in a higher H0 estimate with notable tension with Planck data.

Contribution

It introduces a data-driven approach that relaxes the fixed universal color-luminosity relation, allowing for galaxy-specific extinction laws and assessing their impact on H0.

Findings

H0 estimated at 73.2±1.3 km/s/Mpc with Wesenheit magnitudes.

H0 estimated at 73.9±1.8 km/s/Mpc with galaxy-specific extinction laws.

Tension of 3.4 to 4.2 sigma with Planck's H0 value.

Abstract

Motivated by the large observed diversity in the properties of extra-galactic extinction by dust, we re-analyse the Cepheid calibration used to infer the Hubble constant, $H_0$, from Type Ia supernovae, using Cepheid data in 19 Type Ia supernova host galaxies from Riess et al (2016) and anchor data from Riess et al (2016, 2019, 2021). Unlike the SH0ES team, we do not enforce a fixed universal color-luminosity relation to correct the Cepheid magnitudes. Instead, we focus on a data driven method, where the optical colors and near infrared magnitudes of the Cepheids are used to derive individual color-luminosity relations for each Type Ia supernova host and anchor galaxy. We present two different analyses, one based on Wesenheit magnitudes resulting in $H_0=73.2\pm 1.3$ km/s/Mpc, a $4.2\,\sigma$ tension with the value inferred from the cosmic microwave background. In the second approach, we calibrate an individual extinction law for each galaxy with non-informative priors using color excesses, yielding $H_0=73.9\pm 1.8$ km/s/Mpc, in $3.4\,\sigma$ tension with the Planck value. Although the two methods yield similar results, in the latter approach the Hubble constant inferred from the individual Cepheid absolute distance calibrator galaxies range from $H_0=68.1\pm 3.5$ km/s/Mpc to $H_0=76.7\pm 2.0$ km/s/Mpc. Taking the correlated nature of $H_0$ inferred from individual anchors into account and allowing for individual extinction laws, the Milky Way anchor is in $2.1\,\sigma - 3.1\,\sigma$ tension with the NGC 4258 and the Large Magellanic Cloud anchors, depending on prior assumptions regarding the color-luminosity relations and the method used for quantifying the tension.