First Measurement of the Hubble Constant from Gravitational Wave–Galaxy Cross Correlations

We measure for the first time the Hubble constant ( H 0 ) from the cross correlation of galaxies and gravitational waves (GWs), by applying the Peak Sirens method. This method consists of finding the peak of the 3D angular cross-spectrum C ℓ ( z , D L ) between the galaxy redshifts ( z ) and the GW luminosity distances ( D L ). Using two GW events from the GWTC-3.0 catalog and the GLADE + galaxy catalog, we make the first detection of the cross-correlation peak at 5.9 σ confidence. This signal comes mostly from the best localized event in the catalog, GW190814, which alone provides a 3.4 σ significance. Adding the multimessenger event GW170817, but without using its known redshift, we find H 0 = 6 7 − 15 + 18 km s −1 Mpc −1 and the first observational constraint on the GW bias, b gw < 4.3 at 95% confidence interval. These measurements set the stage for future novel cosmological constraints with this technique.