Evidence of evolution of the black hole mass function with redshift
S. Rinaldi, W. Del Pozzo, Michela Mapelli, A. Lorenzo-Medina, T. Dent
Abstract
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.