Grant: Discovery Grants Program - Individual

Polycyclic Aromatic Hydrocarbons (PAHs) are the largest organic molecules in space playing a crucial role in various chemical and physical processes and also in the prebiotic evolution of life. Their infrared signature, the unidentified infrared (UIR) bands, dominates the appearance of almost all infrared observations. However, although the presence of PAHs in space is now generally accepted, specifics of the emitting population remain elusive. Similarly, although it is firmly established that the detailed characteristics of these UIR bands vary from source to source and spatially within objects, the origin of these variations is not understood. My research will focus on the study of PAHs in galactic and extragalactic environments. My goal is to address the following key questions: How do the characteristics of PAHs (e.g. size, charge) interact with and reflect the physical conditions of their environment (e.g. density, radiation field, temperature)? How can we use the UIR bands as a probe of the physical conditions in regions near and far? What are the characteristics of the long wavelength counterparts to the well-known UIR bands? Specifically, I propose to characterize the variations of the UIR bands at mid- and far-IR wavelengths and calibrate these to the local physical conditions. These include distance from the exciting star, radiation field, electron density, temperature, extinction and metallicity. This will be applied to a wide variety of astronomical objects: star-forming regions, reflection nebulae, the interstellar medium and planetary nebulae. These observational results will subsequently be compared with the NASA Ames PAH IR spectral database containing spectra of a wide range of PAHs and PAH related species. This study is geared towards understanding the underlying causes of the observed variations. In addition, this observational approach provides an empirical calibration of the PAH characteristics with the physical conditions. This in turn, allows us to use of the UIR bands as an environmental diagnostic tool in regions near and far.