Distinguish external and co-spatial scattering line-wing models

Determine whether the exponential emission-line wings in little red dots arise from a scattering medium external to the line-emitting region or from a scattering and line-emitting region that are co-spatial.

Background

The paper discusses exponential emission-line wings as a consequence of repeated photon scattering. Different radiative-transfer geometries predict different detailed line shapes: an external scattering medium produces exponential wings, whereas co-spatial emission and scattering produce broken power-law wings. The paper does not attempt to distinguish these possibilities in either its models or the observations, leaving the geometric origin of the line profiles unresolved.

References

We defer trying to distinguish between these two line profiles in our models (or the data) to future work and refer to the line wings as `exponential' throughout this paper.

— Little Red Dots As Super-Eddington Fountain Flows  (2609.20920 - Kaaz et al., 17 Sep 2026) in Section 1, footnote following the discussion of exponential emission-line wings