Table 4.
Summary of the observed features in the FRESCO-GN-9771 LRD and their interpretation in the context of the black hole star photoionization model.
| Feature | Interpretation in the BH* model | Alternatives/Challenges | Implication |
| Broad wings in Balmer lines | Lines broadened by electron scattering in the warm layer with N(H I, 2s) ≈1016 cm−2. | Alternatively would mainly trace motions in broad-line region. | Virial BH mass scaling relations not applicable. |
| Hα/Hβ = 10.4 ± 0.3(≫2.8) | Indicates collisional excitation, but could also partly be impacted by resonant Hβ scattering, both indicative of very high densities. | Alternatively would imply very high dust attenuation at odds with continuum slope. | Dust corrections based on Balmer decrement are not reliable. Bolometric corrections need revision. |
| P Cygni features in Hα & Hβ | High opacity from layer of warm partially ionized outflowing gas. | Hβ absorption may be unexpectedly stronger than Hα, but could be Hα infilling, or emission at different physical depths. | The outer layer is outflowing†. |
| Shape and strength of Balmer break | High opacity from the turbulent, dense gas in the warm outer layer. | Alternatively, it would require highly unusual stellar populations with almost exclusively A stars. | Optical continuum does not originate from stellar light from the host galaxy, i.e., uncertain stellar masses. |
| Optical [Fe II] forest | Arises from a warm and partially ionized layer with Te = 6000–7500 K. | Photoionized by AGN in an intermediate-density region. | No strong photoionization needed. Broader lines than [O III] point toward different origin (not from a narrow-line region). |
| UV Fe II | Observed absorption troughs compatible with main resonant Fe II multiplets. | Strong UV Fe II emission is possible, but difficult to concile standard templates and models. Overall shape of the UV is very uncertain and different from typical SFGs and AGN. | Deep high-resolution data needed to resolve the UV features. |
| Very narrow [O III] λλ4960,5008 and Hγ emission | Emission from H II regions around young stars of a typical low-mass host galaxy. | No other such narrow lines are convincingly detected. Young stellar cluster associated with the BH? | Suggests that the host galaxy is low mass (Mdyn ∼ 3 × 109 M⊙, Mstar ∼ 108 M⊙). |
| BH mass | Lbol suggests MBH/M⊙ ∼ 0.1 assuming Eddington-rate accretion. Could be even lower if higher accretion rates apply. | Applying standard scaling relations based on Hα would imply MBH/M⊙ > 1. | MBH/M⊙ tension with local relation can be greatly alleviated with reasonable (super-)Eddington ratios. |
| Low He Iλ5876/λ7067 ratio | The model cannot reproduce such relatively strong He Iλ7067 emission. | Pumping contribution and density effects may boost the relative luminosity of λ7067. Better RT models needed. | Showcases Helium lines as an additional probe of the temperature and density structure. |
Notes. †Some LRDs in the literature present redshifted P Cygni, and thus they could be interpreted as inflows. Some show different absorption velocities for different Balmer transitions, indicating complex velocity and opacity effects.
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