A Family Story for Thanksgiving: MAHs, PAHs, & GrandPAHs in Space

Strong IR emission features at 3.3, 6.2, 7.7, 8.6, and 11.2 μm are a common characteristic of regions of massive star formation in the Milky Way and nearby galaxies and out to redshifts of ~3. These features are carried by large (∼ 50 C-atom) Polycyclic Aromatic Hydrocarbon molecules, which are pumped by the strong FUV photon flux from these stars. Observations with ESA’s and NASA’s infrared observatories have revealed the richness of the interstellar infrared emission spectrum and the variations therein. These variations reflect variations in the characteristics of the family of molecules present in space, reflecting the variations in the physical conditions of the emitting regions. However, observations have revealed that the brightest spots in reflection nebulae show highly similar IR emission spectra. This is evidence for the presence of grandPAHs: a set of the most stable PAH species that can survive the harshest conditions of the ISM. I will review the observational evidence and supporting laboratory studies and point out SOFIA's potential contribution and the instrument requirements for such studies.