The Intrinsic Production Rate Part II

The ionizing photon production efficiency, \(\xi_{\rm ion}\), is one of the main quantities we need to calculate for the simulated galaxies (see this post). In Part I I outlined my calculation, and the initial results.

The solution in my previous post wasn’t quite right, so this post includes some corrections, though there is still something wrong!

Calculation

The production efficiency can be calculated as:

\[\xi_{\rm ion} = \frac{\dot{N}_{\rm ion}}{L_{1500}} [\rm Hz/erg ]\]

The rate of ionizing photons is in units [photons/s] not [photons/s/Hz] as I said in the previous post.

Therefore the calculation should be

\[\dot{N}_{\rm ion} = \int_{\nu_{912}}^{\infty} \dfrac{L_\nu}{h \nu} {\rm d} \nu = \int_{0}^{912} \dfrac{L_\nu}{h \lambda} {\rm d} \lambda\]

Additionally, \(L_{1500}\) should be in units of [ergs/s/Hz]. This means I can read this directly from \(L{\nu}\), and don’t need to integrate anything. However, in practice, I take the average \(L_\nu\) value between 1450 and 1550 Angstroms.

Generating the spectrum

I was using the rest-frame spectra. This includes dust, IGM absorption. I should be using intrinsic rest-frame spectra; i.e. the number of photons created before being absorbed by the IGM, or attenuated by dust.

To fix this I set the following:

1. add_igm_absorption=False: turns off the IGM absorption
2. add_agb_dust_model=False: turns off the AGB circumstellar dust model
3. add_dust_emission=False: turns off the Draine & Li 2007 dust emission model.
4. dust_type=0; dust_index=0: sets the dust attenuation curve to a power law, with index 0

Some plots

Here are the values calculated for all the galaxies:

The star-forming galaxies are too low, but the quiescent look okay.

Here are what the spectra look like for 10 example galaxies

One potential problem could be the interpolation to find the flux at 912 Angstroms?

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« Production of Ionizing Photons

The Intrinsic Production Rate Part III »