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Properties of Polycyclic Aromatic Hydrocarbons in the Northwest Photon Dominated Region of NGC 7023. I. PAH Size, Charge, Composition, and Structure DistributionPolycyclic aromatic hydrocarbon (PAH) emission in the Spitzer Infrared Spectrograph spectral map of the northwest photon dominated region (PDR) in NGC 7023 was analyzed exclusively using PAH spectra from the NASA Ames PAH IR Spectroscopic Database (www.astrochem.org/pahdb). The 5-15 micron spectrum at each pixel is fitted using a non-negative-least-squares fitting approach. The fits are of good quality, allowing decomposition of the PAH emission into four subclasses: size, charge, composition, and hydrogen adjacency (structure). Maps tracing PAH subclass distributions across the region paint a coherent astrophysical picture. Once past some 20 seconds of arc from HD 200775, the emission is dominated by the more stable, large, symmetric, compact PAH cations with smaller, neutral PAHs taking over along the lines-of-sight toward the more distant molecular cloud. The boundary between the PDR and the denser cloud material shows up as a distinct discontinuity in the breakdown maps. Noteworthy is the requirement for PANH cations to fit the bulk of the 6.2 and 11.0 micron features and the indication of PAH photo-dehydrogenation and fragmentation close to HD 200775. Decomposition of the spectral maps into "principal" subclass template spectra provides additional insight into the behavior of each subclass. However, the general applicability of this computationally more efficient approach is presently undetermined. This is the first time the spectra of individual PAHs are exclusively used to fit the 5-15 micron region and analyze the spatial behavior of the aromatic infrared bands, providing fundamental, new information about astronomical PAH subpopulations including their dependence on, and response to, changes in local conditions.
Document ID
20140013235
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.1088/0004-637X/769/2/117
Authors
Boersma, C. (San Jose State Univ. Moffett Field, CA, United States)
Bregman, Jesse (Bay Area Environmental Research Inst. Moffett Field, CA, United States)
Allamandola, L. J (NASA Ames Research Center Moffett Field, CA United States)
Date Acquired
October 29, 2014
Publication Date
May 14, 2013
Publication Information
Publication: The Astrophysical Journal
Publisher: IOP
Volume: 769
Issue: 2
Subject Category
Astrophysics
Report/Patent Number
ARC-E-DAA-TN13915
Funding Number(s)
WBS: WBS 399131.02.06.03.49
CONTRACT_GRANT: NNX11AJ33A
CONTRACT_GRANT: NNX12AB89A
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
northwest photon
Hydrocarbon
PAH

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