Mechanism linking UV radiation to PAH molecular size distributions

Identify whether the observed increase in polycyclic aromatic hydrocarbon (PAH) molecular weight with ultraviolet radiation intensity in star formation regions arises from UV‑facilitated PAH formation or from preferential photo‑dissociation of smaller PAH molecules, in order to correctly interpret PAH infrared spectra (e.g., in the coma of 3I/ATLAS) when inferring environmental conditions of origin.

Background

The paper discusses PAH emissions as a potential diagnostic for the origin and environment of interstellar objects, noting that PAH spectral features can inform on molecular size and charge. It highlights trends in star‑forming regions where PAH molecular weights increase with both metallicity and UV radiation intensity.

However, the physical cause of this correlation is uncertain. Resolving whether UV radiation fosters PAH formation or instead selectively destroys smaller PAHs is necessary to interpret observed PAH band ratios (e.g., 3.3/11.2 μm) and to use PAH signatures to constrain the formation environment of 3I/ATLAS and similar objects.