Tabulated optically thin radiative cooling module with Townsend integration

[dutta-alankar]

I have implemented optically thin radiative cooling module for Idefix. I have tested this for by allowing cooling of a collection of cells (initially at $2\times 10^6 \ \rm K$) in a uniform domain (and calculating temperature and $-\dot{e}/n_H^2$ from the code over time) which seems to exactly reproduce the cooling rate as supplied by the table read during runtime by the code (screenshot attached). The setup and analysis code is attached here for reference and further testing. I have also put in a sample Cloudy generated equilibrium cooling rate table for plasma at solar metallicity in presence of HM12 UV photo-ionizing background at redshift 0.

The integration method follows the Townsend algorithm (https://ui.adsabs.harvard.edu/abs/2009ApJS..181..391T/abstract), which is quite efficient in calculating the pressure drop due to radiative cooling. There is also a way to set a floor that switches off cooling below some temperature, as required by many popular setups. I have also included a small .rst documentation for this module.

Let me know if this is something worth integrating to the main repo and if something additional needs to be done.

Test setup:
cooling-test.tar.gz

Test result (purple: supplied table; green: code result):

[dutta-alankar]

@glesur I noticed that use of CGS quantities has now been incorporated into Idefix. If this radiative cooling module with Townsend integration is something you/developer community thinks worth being integrated into Idefix, then I would be happy to change the code to utilize the CGS units capability. Let me know.