Black Hole -- Galaxy Correlations in Simba

We examine the co-evolution of galaxies and supermassive black holes in the simba cosmological hydrodynamic simulation. Simba grows black holes via gravitational torque-limited accretion from cold gas and Bondi accretion from hot gas, while feedback from black holes is modelled in radiative and jet modes depending on the Eddington ratio (f_Edd). Simba shows generally good agreement with local studies of black hole properties, such as the black hole mass–stellar velocity dispersion (M_BH–σ) relation, the black hole accretion rate versus star formation rate (BHAR–SFR), and the black hole mass function. M_BH–σ evolves such that galaxies at a given M_BH have higher σ at higher redshift, consistent with no evolution in M_BH–M_⋆. For MBH≲108M⊙⁠, f_Edd is anticorrelated with M_BH since the BHAR is approximately independent of M_BH, while at higher masses f_Edd–M_BH flattens and has a larger scatter. BHAR versus SFR is invariant with redshift, but f_Edd drops steadily with time at a given M_BH, such that all but the most massive black holes are accreting in a radiatively efficient mode at z≳2⁠. The black hole mass function amplitude decreases with redshift and is locally dominated by quiescent galaxies for M_BH > 10⁸ M_⊙, but for z≳1 star-forming galaxies dominate at all M_BH. The z = 0 f_Edd distribution is roughly lognormal with a peak at fEdd≲0.01 as observed, shifting to higher f_Edd at higher redshifts. Finally, we study the dependence of black hole properties with H i content and find that the correlation between gas content and SFR is modulated by black hole properties, such that higher SFR galaxies at a given gas content have smaller black holes with higher f_Edd.