2024A&A...684A.204R

Aims. We investigate the observed distribution of the joint primary mass, mass ratio, and redshift of astrophysical black holes using the gravitational wave events detected by the LIGO-Virgo-KAGRA collaboration and included in the third gravitational wave transient catalogue.
Methods. We reconstructed this distribution using Bayesian non-parametric methods, which are data-driven models able to infer arbitrary probability densities under minimal mathematical assumptions.
Results. We find evidence that both the primary mass and mass-ratio distribution evolve with redshift: our analysis shows the presence of two distinct subpopulations in the primary mass-redshift plane, with the lighter population, ≲20 M_⊙, disappearing at higher redshifts, z > 0.4. The mass-ratio distribution shows no support for symmetric binaries.
Conclusions. The observed population of coalescing binary black holes evolves with look-back time, suggesting a trend in metallicity with redshift and/or the presence of multiple redshift-dependent formation channels.