Golden and Silver Dark Sirens for precise H0 measurement with HETDEX

TL;DR

This paper evaluates the potential of dark sirens, specifically golden and silver types, combined with HETDEX spectroscopic follow-up, to measure the Hubble constant (H0) with high precision using gravitational wave data.

Contribution

It demonstrates that spectroscopic surveys like HETDEX can enable precise H0 measurements with dark sirens, advancing independent cosmological constraints.

Findings

A single year of VIRUS observations can yield a few-percent H0 constraint.

Golden dark sirens are dominated by a single galaxy, simplifying redshift determination.

Silver dark sirens are more common but have multiple plausible host galaxies.

Abstract

Gravitational waves (GWs) from compact binary coalescences are standard sirens that provide a direct measure of the source's luminosity distance, enabling an independent measurement of the Hubble constant (H0). While a bright siren -- a GW event with an identified electromagnetic (EM) counterpart -- provided the first such constraint, most detections, currently dominated by black hole mergers, lack EM signatures. A measurement of H0 is still possible with these dark sirens by statistically associating GW events with galaxies in existing catalogs based on the sky localization. In this work, we explore the potential of two subsets of sirens: rare golden dark sirens, for which a single galaxy dominates the H0 posterior, and silver dark sirens, which are far more common but have a larger set of plausible host galaxies. Using the fifth internal data release of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), we assess the suitability of the Visible Integral-field Replicable Unit Spectrograph (VIRUS) for spectroscopic follow-up of dark sirens. VIRUS exposures of the standard HETDEX depth provide precise redshifts and exquisite completeness within z = 0.2. After a single year of observations with the upgraded LIGO-A# network, the combined sample of golden and silver dark sirens with z < 0.2 and follow-up VIRUS observations can potentially yield a few-percent constraint on H0. Our predictions suggest that spectroscopic redshift surveys such as HETDEX can play a key role in realizing high-precision cosmology with dark sirens in the near future. Standard-siren distance measurements offer a critical, fully independent path to the local value of H0 to resolve the Hubble tension.