I was wondering if there exists a catalogue of spectral information for the subhalos in IllustrisTNG? I am interested in finding or calculating the H alpha flux for galaxies I have previously identified via their subhalo IDs.
Alternatively, do you know of any studies which have created such a catalog? I have found a few papers describing creating artificial spectral energy distributions for high-redshift galaxies in Illustris (e.g. Figure 3, Shen+20) for their own uses, but am not certain where to go from here.
There are many different ways to try to do this. The most simple would be to apply a conversion factor to convert from star formation rate, to H-alpha. You could apply this either to SubhaloSFR (i.e. one number per object), or at the level of individual gas cells (PartType0/StarFormationRate), which would let you do things like make H-alpha images, calculate radial profiles, etc. This second approach was adopted in Pillepich+ (2019), you can find details and the equation there.
This ignores many complications and details, which may be important, including (dust) obscuration effects. One could also use a radiative transfer post-processing code such as SKIRT to make more accurate predictions for various optical emission lines, but this would be a much more advanced step.
Thanks again for some really useful information. I'll take a look and get to work.