A Measurement of the Hubble Constant using Gravitational Waves from the Neutron-Star Black-Hole Candidate GW190814

Vasylyev, Sergiy; Filippenko, Alex

We present a test of the statistical method introduced by Bernard F. Shutz in 1986 using only gravitational waves to infer the Hubble constant (H$_0$) from GW190814, the first 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 H$_0 = 70^{+35.0}_{-18.0}$ km s$^{-1}$ Mpc$^{-1}$ (maximum a posteriori and 68.3% highest density posterior interval) for a galaxy $B$-band luminosity threshold of $L_B \geq 0.001 L_B^*$ with a correction for catalog incompleteness. Repeating the calculation for GW190814, we obtain H$_0 = 67^{+41.0}_{-26.0}$ km s$^{-1}$ Mpc$^{-1}$ and H$_0 = 71^{+34.0}_{-30.0}$ km s$^{-1}$ Mpc$^{-1}$ for $L_B \geq 0.001 L_B^*$ and $L_B \geq 0.626 L_B^*$, respectively. Combining the posteriors for both events yields H$_0 = 70^{+29.0}_{-18.0}$ 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 H$_0$ values. We repeat the joint inference using the low-spin PhenomPNRT and combined (SEOBNRv4PHM + IMRPhenomPv3HM) posterior samples for GW170817 and GW190814, respectively, achieving a tighter constraint of H$_0 = 69^{+29.0}_{-14.0}$ km s$^{-1}$ Mpc$^{-1}$.