Three regimes of black hole feedback

Douglas Rennehan, Arif Babul, Belaid Moa, Romeel Davé

Published 2023-09-27Version 1

In theoretical models of galaxy evolution, black hole feedback is a necessary ingredient in order to explain the observed exponential decline in number density of massive galaxies. Most contemporary black hole feedback models in cosmological simulations rely on a constant radiative efficiency (usually $\eta \sim 0.1$) at all black hole accretion rates. We present a synthesis model for the spin-dependent radiative efficiencies of three physical accretion rate regimes, i.e. $\eta = \eta(j, \dot{M}_\mathrm{BH})$, for use in large-volume cosmological simulations. The three regimes include: an advection dominated accretion flow ($\dot{M}_\mathrm{BH} < 0.03\,\dot{M}_\mathrm{Edd}$), a quasar-like mode ($0.03 < \dot{M}_\mathrm{BH} / \dot{M}_\mathrm{Edd} < 0.3$), and a slim disc mode ($\dot{M}_\mathrm{BH} > 0.3\,\dot{M}_\mathrm{Edd}$). Additionally, we include a large-scale powerful jet at low accretion rates. The black hole feedback model we present is a kinetic model that prescribes mass loadings but could be used in thermal models directly using the radiative efficiency. We implemented our model into the \texttt{Simba} galaxy evolution model to determine if it is possible to reproduce galaxy populations successfully, and provide a first calibration for further study. Using a $2\times1024^3$ particle cosmological simulation in a $(150\,\mathrm{cMpc})^3$ volume, we found that the model is successful in reproducing the galaxy stellar mass function, black hole mass-stellar mass relationship, and stellar mass-halo mass relationship. Our model shines when we extrapolate to the galaxy group and cluster scale as it impressively predicts the observed baryon fraction within massive groups and low-mass clusters. Moving forward, this model opens new avenues for exploration of the impact of black hole feedback on galactic environments.