The Extragalactic Distance Scale without Cepheids

TL;DR

This paper proposes an alternative method to Cepheids for measuring galaxy distances using the tip of the red giant branch, leading to a slightly higher but consistent estimate of the Hubble Constant.

Contribution

It calibrates the infrared Tully-Fisher relation using red giant branch measurements, providing an independent distance scale without relying on Cepheids.

Findings

Hubble Constant estimate is 10% higher using the red giant branch method.

The two distance scales are consistent within errors.

Additional data needed for conclusive measurements.

Abstract

Distances of galaxies in the Hubble Space Telescope Key Project are based on the Cepheid period-luminosity relation. An alternative basis is the tip of the red giant branch. Using archival HST data, we calibrate the infrared Tully-Fisher relation using 14 galaxies with tip of the red giant branch measurements. Compared with the Key Project, a higher value of the Hubble Constant by 10% +/- 7% is inferred. Within the errors the two distance scales are therefore consistent. We describe the additional data required for a conclusive tip of the red giant branch measurement of H_0.