Envisioning the Distance Ladder in the Era of the Habitable Worlds Observatory

TL;DR

The paper discusses how the Habitable Worlds Observatory can simplify the cosmic distance ladder to achieve 1% precision in measuring the Hubble constant by using advanced stellar distance indicators, reducing reliance on supernovae.

Contribution

It proposes a new approach leveraging HWO's capabilities to measure $H_0$ with only stellar indicators, eliminating the need for the third rung involving supernovae.

Findings

HWO can measure $H_0$ to 1% accuracy using only stellar distance indicators.

Design considerations for telescope and instruments to achieve this goal.

Potential to measure distances to low-mass dwarf galaxies via RR Lyrae stars.

Abstract

The current state-of-the-art cosmic distance ladder requires three rungs--geometric distances, primary indicators, and Type Ia Supernovae--to achieve a 1% measurement of the Hubble constant $H_0$. The Habitable Worlds Observatory will have the sensitivity and resolution to reduce this to a two-step measurement, eliminating the third rung entirely and reaching into the Hubble flow with stellar distance indicators such as Cepheid variables and the tip of the red giant branch alone. We discuss the requirements for a program to measure $H_0$ to 1% with HWO here, including telescope and instrument design considerations. We also comment on the potential of HWO to measure distances to low-mass dwarf galaxies via their RR Lyrae stars.