Nebular Emission Recipe

Our custom nebular emission models are single cloud models, using Cloudy simulations assuming:

• An open geometry

• \(\log U \in [-4, -1.5]\)

• Gas-phase metallicity equal to the stellar metallicity (i.e. the metallicity of the youngest stars)

• Two densities – \(\log n_H = 2\) and \(\log n_H = 3.5\).

• Constant pressure.

For each spectral template, \(Q_0\) is effectively fixed, and thus varying \(\log U\) is equivalent to varying \(R\). We convert the line and continuum intensities produced by Cloudy back into luminosities by solving for the appropriate \(R\) given \(Q_0\), \(\log U\), and \(\log n_H\).

We include the option to add dust grains inside the H II region, which we note produces the effect of extra attenuation and warm dust emission in the emitted continuum in addition to affecting the emitted line ratios.