Constraints on the Cosmic Expansion Rate Using the DECam Local Volume Exploration Survey and the Fifth Gravitational Wave Transient Catalog

Gravitational-wave standard sirens provide a calibration-free measure of distances, offering important input on the long-standing tension between early- and late-Universe measurements of the Hubble constant (H 0). In the absence of an electromagnetic counterpart, the dark siren method can be employed to statistically correlate a gravitational wave event's localization with a galaxy catalog of potential hosts. We present a measurement of the Hubble constant using the DECam Local Volume Exploration Survey Data Release 3 and the fifth Gravitational-Wave Transient Catalog. Applying the dark siren method to a large, photometrically heterogeneous footprint required revised catalog-construction choices: a faint apparent-magnitude threshold (m r<20) to control known photometric-redshift bias, a bright apparent-magnitude threshold (m r>15.5) to exclude saturated sources, implementation of an evolving luminosity function parameterization, and de-biasing survey regions based on survey depth and photometric redshift precision. With these choices applied to DELVE, we obtain H 0= 67.4+13.0-11.2 km,s-1,Mpc-1 from dark sirens alone, and H 0= 70.6+8.7-7.0 km,s-1,Mpc-1 when combined with the bright siren GW170817. We test other galaxy catalog configuration choices, and find subdominant influence from photometric band choice and luminosity function parameterization on the final H 0 posterior. Our results demonstrate that extending the dark siren method to wider-area, non-uniform galaxy surveys is feasible and provides additional constraining power on H 0 relative to the spectral siren method, opening the door for analyses with forthcoming galaxy catalogs from LSST, Euclid, and Roman.