PAHs and the Universe

Driven by ground-based, airborne, and IRAS observations, the PAH hypothesis was first formulated in the mid-eighties : the widespreas emission features in the 3-13 µm range are due to UV-pumped, IR fluorescence by large Polycyclic Aromatic Hydrocarbon molecules.
These molecules are a ubiquitous component of the insterstellar medium both in local galaxies as well as out to redshifts of ~3 and probably beyond, play an important role in its physical and chemical characteristics, and form a key link between small hydrocarbon species and large carbonaceous grains.