Bridging Scales: Modeling Suppressed Bondi Accretion on Black Holes and Its Impact on Galaxy Growth

Abstract The accretion and feedback processes governing supermassive black hole (SMBH) growth span an enormous range of spatial scales, from the Event Horizon to the circumgalactic medium. Recent general relativistic magnetohydrodynamic (GRMHD) simulations demonstrate that strong magnetic fields can substantially suppress gas accretion onto black holes. These simulations show that magnetic fields create magnetically arrested disk states, reducing inflow rates by up to 2 orders of magnitude relative to classical predictions. We incorporate this magnetic suppression prescription from recent GRMHD studies into D ark S age , a semianalytic model that tracks SMBH and galaxy coevolution over cosmic time. Implementing the suppression across different accretion rate regimes, we explore its impact on the distribution of black hole masses, stellar masses in galaxies, and active galactic nucleus (AGN) luminosities. We find that restricting suppression to sub-Eddington accretors ( f Edd < 3 × 10 −3 ) and rescaling AGN feedback efficiencies gives simultaneous agreement with the observed local distributions of both galaxy and black hole masses. At early cosmic times ( z > 6), super-Eddington growth episodes dominate in our model, reproducing the high number densities of luminous AGN recently discovered by the James Webb Space Telescope. Our results highlight the critical sensitivity of galaxy assembly to the coupling between small-scale accretion physics and large-scale feedback regulation. Magnetic suppression of hot gas accretion can reconcile low-redshift constraints while preserving the rapid black hole growth required at early cosmic epochs, thereby providing a physically motivated bridge between horizon-scale GRMHD simulations and cosmological galaxy-formation models.