What's the difference between 'GFM_CoolingRate' in TNG and 'cooling function Lambda' in Sutherland, R. S., & Dopita, M. A. (1993) ?
Yun Wang
28 Apr
Hi Nelson!
In the IllustrisTNG, GFM_CoolingRate is the instantaneous net cooling rate experienced by each gas cell, in cgs units.
Sutherland, R. S., & Dopita, M. A. (1993) also defined a net cooling function, which is defined in terms of the collisional line radiation, free-free and two-photon continuum, recombination processes, photoionization heating, collisional ionization, and Compton heating ( see Eq. (48) in Sec. 3.7 )
So what's the difference between these two cooling functions?
Dylan Nelson
28 Apr
The "net" means "cooling - heating". The involved physics goes beyond Sutherland & Dopita (93) in several ways, and is discussed in the Illustris and TNG methods papers that you find linked in the documentation.
Yun Wang
29 Apr
So does it make sense if I use the method of Sutherland, R. S., & Dopita, M. A. (1993) to calculate the cooling function of gas in TNG using temperature and metallicities?
Dylan Nelson
29 Apr
It's an approximation, that will be ok in some cases, but quite wrong in others. Most clearly, it ignores photoionization and the UVB, which is important at low densities.
Yun Wang
20h
OK, I got it. So is there a good way to compute the 'radiative cooling rate' of gas in TNG?
Dylan Nelson
15h
This is exactly what the GFM_CoolingRate field gives you (for each gas cell).
If you mean, is there a piece of code which computes this for any given gas state, then no, this is all wrapped up in the original simulation code, and there is no standalone function/code.
Yun Wang
9h
You said that the "net" means "cooling - heating", is the 'heating' caused by the feedback process, e.g. AGN and SNe?
Hi Nelson!
In the IllustrisTNG,
GFM_CoolingRateis the instantaneous net cooling rate experienced by each gas cell, in cgs units.Sutherland, R. S., & Dopita, M. A. (1993) also defined a net cooling function, which is defined in terms of the collisional line radiation, free-free and two-photon continuum, recombination processes, photoionization heating, collisional ionization, and Compton heating ( see Eq. (48) in Sec. 3.7 )
So what's the difference between these two cooling functions?
The "net" means "cooling - heating". The involved physics goes beyond Sutherland & Dopita (93) in several ways, and is discussed in the Illustris and TNG methods papers that you find linked in the documentation.
So does it make sense if I use the method of Sutherland, R. S., & Dopita, M. A. (1993) to calculate the cooling function of gas in TNG using temperature and metallicities?
It's an approximation, that will be ok in some cases, but quite wrong in others. Most clearly, it ignores photoionization and the UVB, which is important at low densities.
OK, I got it. So is there a good way to compute the 'radiative cooling rate' of gas in TNG?
This is exactly what the
GFM_CoolingRatefield gives you (for each gas cell).If you mean, is there a piece of code which computes this for any given gas state, then no, this is all wrapped up in the original simulation code, and there is no standalone function/code.
You said that the "net" means "cooling - heating", is the 'heating' caused by the feedback process, e.g. AGN and SNe?