Detection of the Polycyclic Aromatic Hydrocarbon Phenalene (C 13 H 10 ) in the Very Low-luminosity Object MC27/L1521F

Abstract To date, 14 polycyclic aromatic hydrocarbons (PAHs) ranging in size from two to seven (including five- and six-membered) carbon rings have been detected in the starless dense core Taurus molecular cloud (TMC-1 CP). Their detection raises questions about the distribution of PAHs in the cold interstellar medium (ISM) and their evolution during star formation. Here, we present the first interstellar detection of a three-ring PAH outside of TMC-1 CP. We detect phenalene (C 13 H 10 ), a compact, perifused PAH, in the dense core MC27/L1521F, a molecular cloud in Taurus containing a very low-luminosity object. We compare the abundances of phenalene in the two sources with respect to the single-ring aromatic benzonitrile and find that it is enhanced by a factor of 4 in MC27/L1521F. We discuss the implications for possible formation and destruction pathways in the two sources. These findings further support the widespread abundance of PAHs throughout the cold ISM and are consistent with survival, inheritance, or replenishment during the earliest stages of star formation.