Estimate electron density for different metallicities

[fiorella polles]

Hi,

I am using the [SIII]33um/18um ratio to estimate the electron density. I would like to derive the electron density given different metallicities. Is it possible to do it with PyNeb?

Thanks,

Fiorella

[Christophe Morisset]

Hi Fiorella,

The electron density is obtained from a line ratio involving the same ion, in this case S++. Thus the exact value of S++/H+ does not matter, as well as the value of S/H. 

Saludos,

Ch.

[fiorella polles]

Hi Christophe,

I was asking because Kewley et al. 2019 shows in Figure 15 that the infrared [SIII] ratio is sensitive to metallicity for  log_ne < 2.5.

Thanks,

Fiorella

[Christophe Morisset]

Hi Fiorella,

Yes sure, the [SIII] 18/33 line ratio also has a small but not 0 dependency on the temperature. You can see this in the lower-rigth pannel of the 7th figure of this Notebook: https://github.com/Morisset/SIGNALS_lectures/blob/master/Notebooks/3.PyNeb_TeNe.ipynb

In the case one does a complete photoionization model (with constant pressure or constant density) the electron temperature is not fixed, it depends on the metallicity of the nebula: colder for richer gas. Then there is a effect at low density.

The equilibrium temperature in each zone of the nebula is the result of the complex computation done by the photoionization code. This is not what PyNeb is aimed to do. PyNeb is computing the "easy" part of the final step: obtaining the emissivities from Te and Ne, that you can multiply by Xi/H+ and the volume to have the line emission.

In your case, you need to have some Te diagnostic to obtain Te, and then determine Ne from the [SIII] ratio.

Hope it helps,

Christophe

[fiorella polles]

Hi Christophe,

Thank you for the clear explanation! 

Cheers,

Fiorella