Challenges for the statistical gravitational-wave method to measure the Hubble constant

TL;DR

This paper examines the challenges and biases in using gravitational wave data and galaxy surveys to statistically measure the Hubble constant, highlighting limitations of the galaxy voting method.

Contribution

It provides a simulation-based analysis of the galaxy voting method, revealing biases and dependencies affecting the accuracy of Hubble constant estimates.

Findings

Hubble constant posterior is generally biased relative to the true value.

Bias depends on galaxy sample realization and distance measurement precision.

The method's accuracy is limited even under optimistic assumptions.

Abstract

Gravitational waves (GW) can be employed as standard sirens that will soon measure the Hubble constant with sufficient precision to weigh in on the $\sim 5\sigma$ Hubble tension. Most GW sources will have no identified electromagnetic counterpart, leading to uncertainty in the redshift of the source, and in turn a degeneracy between host galaxy distance, redshift, and $H_0$. In the case where no electromagnetic counterparts are identified, it has been proposed that a statistical canvassing of candidate GW hosts, found in a large galaxy survey for example, can be used to accurately constrain the Hubble constant. We study and simulate this "galaxy voting" method to compute $H_0$. We find that the Hubble constant posterior is in general biased relative to the true value even when making optimistic assumptions about the statistical properties of the sample. Using the MICECAT light-cone catalog, we find that the bias in the $H_0$ posteriors depends on the realization of the underlying galaxy sample and the precision of the GW source distance measurement.