First Measurement of the Hubble Constant from a Dark Standard Siren using the Dark Energy Survey Galaxies and the LIGO/Virgo Binary-Black-hole Merger GW170814

We present a multi-messenger measurement of the Hubble constant H <SUB>0</SUB> using the binary-black-hole merger GW170814 as a standard siren, combined with a photometric redshift catalog from the Dark Energy Survey (DES). The luminosity distance is obtained from the gravitational wave signal detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo Collaboration (LVC) on 2017 August 14, and the redshift information is provided by the DES Year 3 data. Black hole mergers such as GW170814 are expected to lack bright electromagnetic emission to uniquely identify their host galaxies and build an object-by-object Hubble diagram. However, they are suitable for a statistical measurement, provided that a galaxy catalog of adequate depth and redshift completion is available. Here we present the first Hubble parameter measurement using a black hole merger. Our analysis results in {H}<SUB>0</SUB>={75}<SUB>-32</SUB><SUP>+40</SUP> {km} {{{s}}}<SUP>-1</SUP> {Mpc}}<SUP>-1</SUP>, which is consistent with both SN Ia and cosmic microwave background measurements of the Hubble constant. The quoted 68% credible region comprises 60% of the uniform prior range [20, 140] km s<SUP>-1</SUP> Mpc<SUP>-1</SUP>, and it depends on the assumed prior range. If we take a broader prior of [10, 220] km s<SUP>-1</SUP> Mpc<SUP>-1</SUP>, we find {H}<SUB>0</SUB>={78}<SUB>-24</SUB><SUP>+96</SUP> {km} {{{s}}}<SUP>-1</SUP> {Mpc}}<SUP>-1</SUP> (57% of the prior range). Although a weak constraint on the Hubble constant from a single event is expected using the dark siren method, a multifold increase in the LVC event rate is anticipated in the coming years and combinations of many sirens will lead to improved constraints on H <SUB>0</SUB>.