Reassessing the Cepheid-based distance ladder: implications for the Hubble constant

Understand

The Hubble constant ($H_0$) is a key parameter in cosmology, yet its precise value remains contentious due to discrepancies between early- and late-universe measurement methods, a problem known as the "Hubble tension." In this study, we revisit the Cepheid-based distance ladder calibration, focusing on two potential sources of bias in the period-luminosity relation (PLR): (1) the assumed prior for the residual parallax offset of the Milky Way (MW) Cepheids and (2) systematic differences between Cepheid periods in anchor galaxies versus supernova host galaxies.

• To address the latter, we adopt two different strategies alongside a renewed MW Cepheid calibration.
• The first strategy involves resampling anchor and host Cepheids from a common distribution of periods.
• This approach provides a conservative estimate of $H_0 = (72.18 \pm 1.76) \, \mathrm{km/s/Mpc}$, including the renewed MW analysis.