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 (GW), by applying the Peak Sirens method. This method consists of finding the peak of the 3D angular cross-spectrum C(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 sigma confidence. This signal comes mostly from the best localized event in the catalog, GW190814, which alone provides a 3.4 sigma significance. Adding also the multimessenger event GW170817, but without using its known redshift, we find H 0 = 67+18-15 km s-1 Mpc-1 and the first observational constraint on the GW bias, b gw < 4.3 at 95% CI. These measurements set the stage for future novel cosmological constraints with this technique.