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jacobseiler / rsage

The Reionization using Semi-Analytic Galaxy Evolution model.
MIT License
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Started working on updating the quasar model. #3

Closed jacobseiler closed 6 years ago

jacobseiler commented 6 years ago

Going to keep a log of my changes in this pull request. Hopefully it will be easier to lay out my thoughts and put some plots here for direct comparison.

The biggest thing is that following a merger event, the central galaxy BH accretes cold gas instantly. While this is ok for something like Millennium, I'm worried that this won't be applicable for Kali.

To this end, in this new model I follow something similar to Qin 2017's implentation in MERAXES. I calculate the amount of mass that should be accreted by the black hole then compare that to the Eddington Mass. If the Eddington Mass is greater than the accreted mass then all the mass will be accreted in a timestep otherwise only mass equal to the Eddington Mass will be accreted. Regardless of this, I spread this mass accreted over the substeps.

In addition to altering the accretion rate to be smooth, I also include the fractional quasar ejection. During each accretion event I say that a quasar pulses with energy from the amount of mass accreted. Then I compare this amount of energy with the thermal energy of the reservoirs and eject/reheat mass proportional to the RATIO of the quasar energy to the thermal energies.

jacobseiler commented 6 years ago

bhmodels_paper Form the first implementation of the model it seems that there is simply just too little feedback. This isn't too surprising as instead of the quasars going off with one big burst of energy, there's a lot of smaller ones.

Although as I write this I'm not sure that actually makes logical sense. Because the amount of energy that is emitted SHOULD be the same; the black hole is still accreting the same amount of mass but it's over a longer time. I'll have a look at the new variable BHmass_accrete_thisstep and see how it compares to the values that are accreted in the oldBH model.

jacobseiler commented 6 years ago

bhmodels_paper

Fixed up the calculations. Problem was I was dividing rather than multiplying by eddington_factor and forgot to convert my dt into Myr.

The SMF looks similar to as they did before but there is a bit of a dip at the high mass end compared to before. This points to the fact that perhaps there is just too little feedback occurring. I'll tinker with the parameters and see what happens.

jacobseiler commented 6 years ago

This update (or at least this approach) may need to be shelved for now. I've realised that by moving to this smooth accretion history that there would now be an inconsistency between how the mergers are handled. This is because currently when two galaxies "merge" their reservoirs are added together instantly (along with the instant burst of SF and growth of the black hole). If I move to a regime where the BH accretion happens smoothly, perhaps I need to also revisit the assumptions regarding the integration of the satellite reservoirs.

I've also just realised that by inducing a smooth accretion, the accretion rate will not be constant over a single timestep. But rather as the black hole accretes mass, the accretion rate in the next substep should also increase to account for the increased gravitational force.

There's a lot of tangled up effects here that I'm not sure I want to touch. It would be a massive undertaking to do this all systematically and correctly, something I'm not sure I have the time (or patience tbh) for...