Carrier of the 16.4 Micron Sub-Feature and Underlying Continuum

Determine the detailed carrier of the 16.4 μm sub-feature and the underlying continuum within the 17 μm emission complex observed in NGC 7023.

Background

The paper discusses a broad 15–18 μm emission feature in NGC 7023 that forms part of the 17 μm complex, including resolved components near 16.4 and 17.4 μm. Although the 17.4 μm component is commonly attributed to neutral C60 fullerenes, the paper explicitly states that the detailed carrier of the 16.4 μm component and the underlying continuum have not been settled. The authors suggest that curved, defect-rich carbon networks could contribute to this emission through enhanced out-of-plane skeletal modes, but they do not establish these species as the definitive carriers.

References

While the \SI{17.4}{\micro\meter} feature is commonly attributed to neutral $C_{60}$ fullerenes \citep{Cami2010, Sellgren2010}, the detailed carrier of the \SI{16.4}{\micro\meter} sub-feature and the underlying continuum remain debated.

— Beyond Idealized PAHs: Infrared Signatures of Carbon-Chain Defects from Shock Synthesis  (2608.18505 - Tan et al., 19 Aug 2026) in Section 4, Observational Implications