2014ApJ...794...83C

Recent studies have confirmed the presence of buckminsterfullerene (C₆₀) in different interstellar and circumstellar environments. However, several aspects regarding C₆₀ in space are not yet well understood, such as the formation and excitation processes, and the connection between C₆₀and other carbonaceous compounds in the interstellar medium, in particular polycyclic aromatic hydrocarbons (PAHs). In this paper, we study several photodissociation regions (PDRs) where C₆₀and PAHs are detected and the local physical conditions are reasonably well constrained to provide observational insights into these questions. C₆₀is found to emit in PDRs where the dust is cool (T_d= 20-40 K) and even in PDRs with cool stars. These results exclude the possibility for C₆₀to be locked in grains at thermal equilibrium in these environments. We observe that PAH and C₆₀emission are spatially uncorrelated and that C₆₀is present in PDRs where the physical conditions (in terms of radiation field and hydrogen density) allow for full dehydrogenation of PAHs, with the exception of Ced 201. We also find trends indicative of an increase in C₆₀ abundance within individual PDRs, but these trends are not universal. These results support models where the dehydrogenation of carbonaceous species is the first step toward C₆₀formation. However, this is not the only parameter involved and C₆₀formation is likely affected by shocks and PDR age.