Resolve the role of H-alpha resonant trapping in Paschen-continuum signatures

Determine how resonant scattering and trapping of H$\alpha$ photons affect the hydrogen $n=3$ population, Paschen-continuum opacity, and predicted Paschen-break signatures in the densest little-red-dot wind models.

Background

The densest models are marginally opaque to the Paschen continuum and show possible Paschen bound-free absorption. These predictions depend sensitively on the Hα\alpha trapping treatment, which in turn is affected by the Sobolev approximation. A more accurate treatment is needed to determine whether the predicted Paschen features are physical and whether they imply an extreme subclass of Paschen-break sources.

References

We caveat that this is affected by H$\alpha$ trapping, which may be affected by the Sobolev approximation (see Sec.~\ref{sec:caveats}) and should be explored further in a later work.

— Little Red Dots As Super-Eddington Fountain Flows  (2609.20920 - Kaaz et al., 17 Sep 2026) in Section 5.5, “Photoionization of the Wind”