Simulations of black hole fueling in isolated and merging galaxies with
  an explicit, multiphase ISM
  We study gas inflows onto supermassive black holes using hydrodynamics
simulations of isolated galaxies and idealized galaxy mergers with an explicit,
multiphase interstellar medium (ISM). Our simulations use the recently
developed ISM and stellar evolution model called Stars and MUltiphase Gas in
GaLaxiEs (SMUGGLE). We implement a novel super-Lagrangian refinement scheme
that increases the gas mass resolution in the immediate neighborhood of the
black holes (BHs) to accurately resolve gas accretion. We do not include black
hole feedback in our simulations. We find that the complex and turbulent nature
of the SMUGGLE ISM leads to highly variable BH accretion. BH growth in SMUGGLE
converges at gas mass resolutions $\lesssim3\times10^3{\rm M_\odot}$. We show
that the low resolution simulations combined with the super-Lagrangian
refinement scheme are able to produce central gas dynamics and BH accretion
rates very similar to that of the uniform high resolution simulations. We
further explore BH fueling by simulating galaxy mergers. The interaction
between the galaxies causes an inflow of gas towards the galactic centres and
results in elevated and bursty star formation. The peak gas densities near the
BHs increase by orders of magnitude resulting in enhanced accretion. Our
results support the idea that galaxy mergers can trigger AGN activity, although
the instantaneous accretion rate depends strongly on the local ISM. We also
show that the level of merger-induced enhancement of BH fueling predicted by
the SMUGGLE model is much smaller compared to the predictions by simulations
using an effective equation of state model of the ISM.
