On the viability of the PAH model as an explanation of the unidentified infrared emission features

Abstract

Polycyclic aromatic hydrocarbon (PAH) molecules are widely considered as the preferred candidate for the carrier of the unidentified infrared emission bands observed in the interstellar medium and circumstellar envelopes. In this paper we report the result of fitting a variety of non-PAH spectra (silicates, hydrogenated amorphous carbon, coal and even artificial spectra) using the theoretical infrared spectra of PAHs from the NASA Ames PAH IR Spectroscopic Database. We show that these non-PAH spectra can be well fitted by PAH mixtures. This suggest that a general match between astronomical spectra and those of PAH mixtures does not necessarily provide definitive support for the PAH hypothesis.

arXiv comment19 pages, 9 figures, accepted for publication in ApJ

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• A Small Fullerene (C24) may be the Carrier of the 11.2 micron Unidentified Infrared Band
• Petroleum, coal and other organics in space
• Deuterated Polycyclic Aromatic Hydrocarbons in the Interstellar Medium: The C--D Band Strengths of Multi-Deuterated Species
• Laser-Induced Electronic and Vibronic Dynamics in the Pyrene Molecule and its Cation
• The 6 $\mu$m Feature as A Tracer of Aliphatic Components of Interstellar Carbonaceous Grains
• GTC/CanariCam mid-IR imaging of the fullerene-rich Planetary Nebula IC 418: searching for the spatial distribution of fullerene-like molecules
• Infrared spectra of solid indene pure and in water ice. Implications for observed IR absorptions in TMC-1
• Molecular studies of Planetary Nebulae
• On the formation of molecules and solid-state compounds from the AGB to the PN phases