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

TL;DR

This study demonstrates that non-PAH spectra can be accurately fitted with PAH mixtures, challenging the assumption that spectral matches confirm PAHs as the carriers of unidentified infrared emission features.

Contribution

The paper shows that non-PAH spectra can be modeled with PAH mixtures, questioning the specificity of spectral matches for confirming PAH presence in space.

Findings

Non-PAH spectra can be well fitted by PAH mixtures.

Spectral matches do not necessarily confirm PAHs as carriers.

PAH models may fit a variety of non-PAH spectra.

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.