Resolving flows around black holes: the impact of gas angular momentum

Cosmological simulations almost invariably estimate the accretion of gas on to supermassive black holes using a Bondi-Hoyle-like prescription. Doing so ignores the effects of the angular momentum of the gas, which may prevent or significantly delay accreting material falling directly on to the black hole. We outline a black hole accretion rate prescription using a modified Bondi-Hoyle formulation that takes into account the angular momentum of the surrounding gas. Meaningful implementation of this modified Bondi-Hoyle formulation is only possible when the inner vorticity distribution is well resolved, which we achieve through the use of a super-Lagrangian refinement technique around black holes within our simulations. We then investigate the effects on black hole growth by performing simulations of isolated as well as merging disc galaxies using the moving-mesh code AREPO. We find that the gas angular momentum barrier can play an important role in limiting the growth of black holes, leading also to a several Gyr delay between the starburst and the quasar phase in major merger remnants. We stress, however, that the magnitude of this effect is highly sensitive to the thermodynamical state of the accreting gas and to the nature of the black hole feedback present.MC is supported by the Science and Technology Facilities Council (STFC). DS acknowledges support by the STFC and the ERC Starting Grant 638707 ‘Black holes and their host galaxies: co-evolution across cosmic time’. This work was performed on the following: the COSMOS Shared Memory system at DAMTP, University of Cambridge operated on behalf of the STFC DiRAC HPC Facility – this equipment is funded by BIS National E-infrastructure capital grant ST/J005673/1 and STFC grants ST/H008586/1, ST/K00333X/1; DiRAC Darwin Supercomputer hosted by the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/), provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and funding from the Science and Technology Facilities Council; DiRAC Complexity system, operated by the University of Leicester IT Services. This equipment is funded by BIS National E-Infrastructure capital grant ST/K000373/1 and STFC DiRAC Operations grant ST/K0003259/1; COSMA Data Centric system at Durham University, operated by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility. This equipment was funded by a BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grant ST/K00087X/1, DiRAC Operations grant ST/K003267/1 and Durham University. DiRAC is part of the National E-Infrastructure