CARMA OBSERVATIONS OF PAH RICH SOURCES: NGC 2023, L134N AND GGD 27
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Date
2013
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Publisher
Ohio State University
Abstract
Polycyclic aromatic hydrocarbons (PAHs) and polycyclic aromatic nitrogen heterocycles (PANHs) have been the focus of intense astrochemical interest in recent years. PA(N)Hs account for up to 20\% of the interstellar carbon budget and are believed to play key roles in many chemical and physical processes in the ISM. Evaluation of the extent to which PA(N)Hs influence these processes is hampered by our inability to detect PA(N)Hs concurrently with other chemical species using radio astronomy, due to their low dipole moments and large partition functions. An alternative is to observe regions with previous infrared detection and mapping of PA(N)Hs and correlate radio and infrared observations. We have conducted 3 mm CARMA C and D configuration observations of three PA(N)H rich sources that have been previously observed in the infrared: NGC 2023, L134N, and GGD 27. We will report the results of our analysis in the context of PA(N)H observations. %While the evidence for their existence, as well as their importance to interstellar chemistry, is clear, to date only two such molecules have been individually detected in the ISM: C$_{60}$ and C$_{70}$, owing to inherent structural similarities between these species that results in characteristic, but ambiguous, spectral signatures in infrared observations. %PAHs are formed through reactions of acetylene (C$_2$H$_2$) and other small organic molecules; PANHs form through analogous reactions with HCN. Detection of individual PAHs is necessary to test models and assumptions of PAH evolution and key to furthering our understanding of the role PAHs play in astronomical processes. Radio astronomy and gas phase rotational spectroscopy provide the tools necessary for unambiguous identification of these molecules in interstellar environments, however, such detections have not yet been achieved. %Our goal is to mapping the distributions of HCN, HCO$^+$, CH$_3$OH, and CO in selected sources using combined. By correlating the local carbon and HCN abundances, temperatures, and ionizing radiation flux in these environments, we can identify "goldilocks" regions which should highly favor the existence of gas phase PA(N)Hs. Such information will be vital for follow-up searches for individual PANHs using CARMA and ALMA. We have chosen three distinct sources known or predicted to have high abundances of PA(N)Hs as a starting point: NGC 2023, L134 N, and GGD 27.
Description
Author Institution: Department of Chemistry, California Institute of Technology, Pasadena CA, 91125; Divisions of Geological and Planetary Sciences and Chemistry and Chemical Engineering, California Institute of Technology, Pasadena CA, 91125