Measuring the Hubble constant with a gravitational wave black-hole merger and the Dark Energy Survey

In this talk I will present the first measurement of the Hubble constant using a binary black hole gravitational wave detection from LIGO/Virgo (GW170814) and the Dark Energy Survey (DES) galaxy catalog. The DES collaboration has a dedicated effort to follow up gravitational wave events, and it led to the discovery of the kilonova associated to GW170817. Our team has also followed up GW170814, but we found no compelling evidence for an electromagnetic counterpart. In order to use GW170814 as a standard siren and measure the Hubble constant in the absence of a host galaxy redshift, we applied a statistical method that takes into account all the potential host galaxies observed with DES. The precision on the Hubble constant from a single event of this kind is close to 48% (68% confidence level), but we anticipate a multifold increase on the LIGO/Virgo event detection rate in the coming years. The synergy between gravitational wave detections with and without an associated electromagnetic counterpart, and large galaxy surveys will allow precision cosmology studies in the very near future.