Measurement of the Hubble constant using the Dark Energy Survey Year 6 Gold galaxy catalog and the fourth Gravitational-Wave Transient Catalog

Gravitational wave standard sirens enable independent measurements of the Hubble constant $H_0$. In the absence of electromagnetic counterparts, the “dark siren” method statistically correlates GW events with potential host galaxies. We present a measurement of $H_0$ using 142 compact binary coalescences from the fourth Gravitational-Wave Transient Catalog (GWTC-4.0) combined with the Dark Energy Survey Year 6 Gold photometric galaxy catalog. Using the gwcosmo pipeline, we jointly infer cosmological and GW population parameters. We analyze the impact of galaxy catalog properties on the inference, identifying significant features in the galaxy redshift distribution which can introduce biases. By restricting the galaxy catalog to $0.05<z<0.35$ to maintain consistency with a uniform in comoving volume galaxy distribution, we obtain a result of $H_0 = 70.9^{+22.3}{-18.6};\text{km};\text{s}^{-1};\text{Mpc}^{-1}$ from dark sirens and $H_0=73.1^{+11.7}{-8.6};\text{km};\text{s}^{-1};\text{Mpc}^{-1}$ when combined with the bright siren GW170817. This study demonstrates the adaptation of deep galaxy catalogs for GW cosmology, highlighting key challenges and methodologies essential for maximizing the potential of next-generation galaxy surveys.

💡 Research Summary

This paper presents a comprehensive measurement of the Hubble constant (H_{0}) using the “dark siren” technique, which statistically associates gravitational‑wave (GW) events without electromagnetic counterparts to potential host galaxies. The authors combine 142 compact binary coalescence (CBC) detections from the fourth Gravitational‑Wave Transient Catalog (GWTC‑4.0) with the Dark Energy Survey Year 6 Gold (DES Y6 Gold) photometric galaxy catalog.

The analysis is performed with the publicly available gwcosmo pipeline, a Bayesian framework that simultaneously infers cosmological parameters (primarily (H_{0}) and (\Omega_{m})) and CBC population parameters (mass spectrum, merger rate evolution, etc.). A key ingredient is the line‑of‑sight (LOS) redshift prior, which encodes the redshift distribution of galaxies within each HEALPix pixel. The authors construct this prior by summing two contributions: (i) a catalog term that treats each galaxy as a Gaussian in redshift with width given by its photometric‑z uncertainty, and (ii) an “empty‑catalog” term that assumes galaxies missing from the catalog are uniformly distributed in comoving volume.

To make the DES catalog “cosmology‑ready,” several quality cuts are applied: non‑null photometry in the griz bands, FLAGS_FOOTPRINT = 1, FLAGS_FOREGROUND = 0, and FLAGS_GOLD = 0, which together remove 19 % of the original 669 million objects. The authors adopt the BDF (bulge+disk) photometric model and use r‑band magnitudes because they have the smallest photometric errors. Completeness is assessed via the r‑band luminosity function; the catalog is essentially 100 % complete to (z\approx0.5) for absolute magnitudes (M_{r}<-17.5).

A weighting scheme for host‑galaxy probability is introduced:
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