2020ApJ...902..149V

We present a test of the statistical method introduced by Bernard F. Shutz in 1986 using only gravitational waves to infer the Hubble constant (H₀) from GW190814, the first high-probability neutron-star-black hole (NS-BH) merger candidate detected by the Laser Interferometer gravitational-wave Observatory (LIGO) and the Virgo interferometer. We apply a baseline test of this method to the binary neutron star (BNS) merger GW170817 and find H₀=70_–18.0^+35.0 km s^–1 Mpc^–1 (maximum a posteriori and 68.3% highest density posterior interval) for a galaxy B-band luminosity threshold of L_B≥ 0.001L_B^* with a correction for catalog incompleteness. Repeating the calculation for GW190814, we obtain H₀=67_–26.0^+41.0 km s^–1 Mpc^–1 and H₀=71_–30.0^+34.0 km s^–1 Mpc^–1 for L_B≥ 0.001L_B^* and L_B≥ 0.626L_B^* , respectively. Combining the posteriors for both events yields H₀=70_–18.0^+29.0 km s^–1 Mpc^–1, demonstrating the improvement on constraints when using multiple gravitational-wave events. We also confirm the results of other works that adopt this method, showing that increasing the L_B threshold enhances the posterior structure and slightly shifts the distribution's peak to higher H₀ values.We repeat the joint inference using the low-spin PhenomPNRT and the newly available combined (SEOBNRv4PHM + IMRPhenomPv3HM) posterior samples for GW170817 and GW190814, respectively, achieving a tighter constraint of H₀=69_–14.0^+29.0 km s^–1 Mpc^–1.