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Update to the spin/jet AGN model, March 2024

Filip Husko requested to merge spin_jet_updates_March2024 into master

@matthieu Here is the update I was mentioning. It is overall not as bad as I thought in terms of overall size. Here is a summary of the main changes.

  1. Update to how the final BH-BH merger spin is calculated. The numerical relativity papers with fitting functions typically give a formula for the final spin magnitude, which I was using. I was also assuming that the final spin direction corresponds to the direction of (in vector form) J_spin_1 + J_spin_2 + L_orb (the total angular momentum of the two spins + orbital angular momentum). This bit is very wrong, since the orbital angular momentum in the simulations dominates over everything else. In the new approach, I use a vector equation for the final spin (which is also given by the papers). This gives both its magnitude and direction correctly, matching the numerical relativity simulations.

  2. I added wind efficiencies in the thick and slim disc (low and super-Eddington rates). These are implemented simply as thermal feedback, alongside the 'radiative'/quasar channel used in the thin disc, with everything being exactly the same, except the efficiencies. Technically, the thin disc feedback mode is also a wind, so there really isn't any distinction here, it's just a matter of what launches the wind (gas/MHD/radiation pressure), but they are all thermalized on subgrid scales. I have added additional tracer fields to keep track of how much energy is dumped in the wind mode, as well as in radiation, so things can be separated/analyzed in postprocessing.

  3. The definition of the Eddington ratio (for this model) has been changed to the spin-dependent one, to be more consistent with recent papers.

  4. The accretion/feedback modes are now switched immediately upon the calculation of the new Eddington ratio. This means that how much energy is being injected now matches which mode the BH is actually in, but the length of the current time-step may be too short or too long to represent one heating/kicking event. I am not sure what would be the best way to take care of that. But switching modes immediately is at least energetically more conservative.

  5. Some updates to the accretion efficiency. I have added a slim disc (super-Eddington) efficiency, as well as an option of an Eddington-ratio dependent accretion efficiency in the thick disc (as motivated by simulations).

  6. Added update to how jet efficiencies and spindown are calculated in the super-Eddington regime, as based on new GRMHD simulations. These same simulations predict non-negligible effects at sub-Eddington rates, so there is an option to apply this also in that regime.

  7. Modified the scaling of the jet velocity with BH mass to reflect what is being done for COLIBRE.

  8. Added two new tracer fields for jet kicking events. When a gas particle is kicked, it now knows which BH kicked it, and which accretion/feedback mode the BH was in when it did so. This will be extremely useful for analyses later on, especially for creation of radio images, which I hope to do.

Some things to do before merging:

  • update parameter files
  • update documentation

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