Abstract

Dwarf galaxies are ideal laboratories to probe the interplay between galaxy formation and the growth of black holes (BHs) in the early Universe. Mounting observational evidence reveals the presence of BHs in low-mass galaxies across cosmic time, with JWST uncovering a likely population of overmassive BHs at 2 ≲ z ≲ 11. Simulations struggle to reproduce this high-redshift regime, motivating revisions to BH accretion and active galactic nucleus (AGN) feedback modelling. We present high-resolution cosmological zoom-in simulations of a dwarf galaxy based on FABLE physics, introducing novel sink-based BH accretion models and relaxing the fiducial assumption of strong supernova feedback. BHs accrete more efficiently in the sink-based runs compared to the ‘traditional’ Bondi-based counterparts, while the impact of AGN feedback on star formation ranges from negligible to early (z ≳ 2) and rapid quenching maintained by fast, hot outflows down to z = 0. We further assess the performance of two widely used dynamical mass estimators and find significant departures from the true dynamical mass, especially during the high-redshift dwarf assembly. Since our galaxy is dark-matter-dominated at all times and radii, BH growth, tied to the baryon cycle, shows no clear correlation with global dynamical properties. Simulations with efficient AGN feedback yield overmassive BHs relative to extrapolated local BH mass − stellar mass scaling relations, hinting at a potential connection between dormant BHs in local dwarfs and high-redshift JWST B Hs. High-redshift feedback from rapidly assembled, overmassive BHs drives metal-enriched outflows that pollute the outer circumgalactic medium, leading to flat metallicity gradients that persist down to z = 0.