I'm calculating dust corrected luminosities for stellar particles using the model(C) in the paper Nelson+19. But for subhalos without any gas (ex. subhalo id 1572823 in snapshot 99 in tng300-1) do you know how should I implement dust correction model? Thanks
If a subhalo has no gas, then N_H = 0 (in Eqn. 4) by definition. So the "resolved dust" component of Model C would be zero. Note however that this component is in addition to the "unresolved dust" component from Model B, which would still apply (although, if a subhalo has no gas, it likely has no stars younger than 10 Myr, i.e. only the second line of Eqn. 1 would apply).
N_H = 0
However, keep in mind that it is somewhat impossible that a subhalo actually has no gas (along a given line of sight). If e.g. you are considering a satellite subhalo, then it is embedded within the gas of its parent FoF halo, which could be used for this calculation. Even if you are considering a central subhalo without gas (e.g. likely a backsplash galaxy), then there would be "IGM" along the line of sight. In both cases, however, it is likely that the resulting N_H would be vanishingly small, and thus that the "resolved dust" contribution would be negligible.