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Harvard ADS: The effects of super-Eddington accretion and feedback on the growth of early supermassive black holes and galaxies

Paper abstract: We present results of cosmological zoom-in simulations of a massive protocluster down to redshift z~4 (when the halo mass is ~10^{13} M_\odot) using the SWIFT code and the EAGLE galaxy formation model, focusing on supermassive black hole (BH) physics. The BH was seeded with a mass of 10^4 M_\odot at redshift z~17. We compare the base model that uses an Eddington limit on the BH accretion rate and thermal isotropic feedback by the AGN, with one where super-Eddington accretion is allowed, as well as two other models with BH spin and jets. In the base model, the BH grows at the Eddington limit from z=9 to z=5.5, when it becomes massive enough to halt its own and its host galaxy's growth through feedback. We find that allowing super-Eddington accretion leads to drastic differences, with the BH going through an intense but short super-Eddington growth burst around z~7.5, during which it increases its mass by orders of magnitude, before feedback stops further growth (of both the BH and the galaxy). By z~4 the galaxy is only half as massive in the super-Eddington cases, and an order of magnitude more extended, with the half-mass radius reaching values of a few physical kpc instead of a few hundred pc. The BH masses in our simulations are consistent with the intrinsic BH mass-stellar mass relation inferred from high-redshift observations by JWST. This shows that galaxy formation models using the \LambdaCDM cosmology are capable of reproducing the observed massive BHs at high redshift. Allowing jets, either at super- or sub-Eddington rates, has little impact on the host galaxy properties, but leads to lower BH masses as a result of stronger self-regulation, which is itself a consequence of higher feedback efficiencies.