BH merger rates in the first billion years in light of JWST discoveries

Recent James Webb Space Telescope (JWST) discoveries have unveiled an abundance of faint and massive Active Galactic Nuclei (AGNs) at high redshifts (z=4-9), that surpass by 10-100 times the extrapolated bolometric (Bol) and ultraviolet (UV) luminosity functions (LF) from previous AGN surveys. Two main models are proposed to explain these observations: light seeds (˜150???) accreting in episodes of super Eddington luminosity, and heavy seeds (˜ 10^3 - 10^5???) growing at the Eddington limit. Future gravitational observatories like the Laser Interferometer Satellite Antenna (LISA) will disentangle these models by detecting BH-BH merger events from mid to high redshifts. We report BH-BH merger rates in the heavy seed scenario using Delphi, a semi-analytical model that tracks baryonic physics across cosmic time through the hierarchical evolution of dark matter halos, down to z=5. In our models, we explore both instantaneous and delayed BH merging, as well as extreme spin configurations (a=0.99, a=-0.99) to bracket BH mass growth.