Velocity correction for Hubble constant measurements from standard sirens

Gravitational wave (GW) sources are an excellent probe of the luminosity distance and offer a novel measure of the Hubble constant, H₀. This estimation of H₀ from standard sirens requires an accurate estimation of the cosmological redshift of the host galaxy of the GW source after correcting for its peculiar velocity. The absence of an accurate peculiar velocity correction affects both the precision and accuracy of the measurement of H₀, particularly for nearby sources. Here, we propose a framework to incorporate such a peculiar velocity correction for GW sources. A first implementation of our method to the event GW170817, combined with observations taken with Very Large Baseline Interferometry (VLBI), leads to a revised value of H₀ = 68.3_-4.5^+4.6 km s^-1 Mpc^-1. While this revision is minor, it demonstrates that our method makes it possible to obtain unbiased and accurate measurements of H₀ at the precision required for the standard siren cosmology.