Exploring supermassive black hole physics and galaxy quenching across halo mass in FIRE cosmological zoom simulations

Feedback from accreting supermassive black holes (SMBHs) is thought to be a primary driver of quenching in massive galaxies, but how to best implement SMBH physics into galaxy formation simulations remains ambiguous. As part of the Feedback in Realistic Environments (FIRE) project, we explore the effects of different modelling choices for SMBH accretion and feedback in a suite of ∼500 cosmological zoom-in simulations across a wide range of halo mass (10¹⁰-10¹³ M_☉). Within the suite, we vary the numerical schemes for BH accretion and feedback, accretion efficiency, and the strength of mechanical, radiative, and cosmic ray feedback independently. We then compare the outcomes to observed galaxy scaling relations. We find several models satisfying observational constraints for which the energetics in different feedback channels are physically plausible. Interestingly, cosmic rays accelerated by SMBHs play an important role in many plausible models. However, it is non-trivial to reproduce scaling relations across halo mass, and many model variations produce qualitatively incorrect results regardless of parameter choices. The growth of stellar and BH mass are closely related: for example, overmassive BHs tend to overquench galaxies. BH mass is most strongly affected by the choice of accretion efficiency in high-mass haloes, but by feedback efficiency in low-mass haloes. The amount of star formation suppression by SMBH feedback in low-mass haloes is determined primarily by the time-integrated feedback energy. For massive galaxies, the 'responsiveness' of a model (how quickly and powerfully the BH responds to gas available for accretion) is an additional important factor for quenching.