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 the best way to 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 modeling choices for SMBH accretion and feedback in a suite of
$\sim500$ cosmological zoom-in simulations across a wide range of halo mass
(10^10-10^13 Msun). Within the suite, we vary the numerical schemes for BH
accretion and feedback, the 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 that
satisfy the observational constraints, and for which the energetics in
different feedback channels are physically plausible. Interestingly, cosmic
rays accelerated by SMBHs play an important role in many successful 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, over-massive BHs tend to over-quench galaxies. BH mass is most
strongly affected by the choice of accretion efficiency in high-mass halos, but
by feedback efficiency in low-mass halos. The amount of star formation
suppression by SMBH feedback in low-mass halos is determined primarily by the
time-integrated feedback energy. For massive galaxies, the "responsiveness" of
a model (i.e. how quickly and powerfully the BH responds to gas available for
accretion) is an additional important factor for quenching.
