Linking visible absorption bands and far-IR emission features trough MonteCarlo simulations: a quantitative test of the PAHs DIBs-UIBs hypothesis
Abstract
One important aspect which is seldom emphasized on the so-called ``strong'' Polycyclic Aromatic Hydrocarbons (PAHs) hypothesis is that the failure to identify the vibronic absorption bands of PAH cations and/or radicals in the visible would cast strong doubts on the applicability of the PAH model for the UIBs and on their alleged presence in the ISM at all.
In order to quantitatively assess this link between DIBs and UIBs, we modeled the interaction of a big, isolated PAH molecule with the interstellar radiation field, which in the PAH model is supposed to govern both the intensities of the UIBs and the spectral profile of its vibronic absorption bands, as given by its rotational envelope. We used a MonteCarlo approach, tailored on the properties of a specific molecule and on the interstellar environment it is embedded in. As a ``proof of concept'' case, we considered the cation of a middle sized PAH, namely the ovalene molecule (C32H14+): we obtained the expected rotational profile of its first allowed electronic transition D0 to D2, which falls at about 9700Å, as a function of a grid of widely different ambient radiation fields. Our results, which can be expected to hold for other similar PAHs, show that the band profiles are remarkably insensitive to both the ambient conditions and the assumed values of some key molecular parameters. This provides a sound quantitative foundation to the hypothesis of PAHs as DIB carriers, since the profile invariance with respect to diverse physical environments is one of the most prominent observed DIB properties. We also obtained a quantitative relation between the modeled ``DIB'' and the far infrared emission bands, both of which are a peculiar fingerprint of each and every specific molecule. This result provides a very powerful criterion for the identification of specific PAHs, both in the presently available ISO data and in those of the forthcoming SIRTF mission.- Publication:
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Astrophysics of Dust
- Pub Date:
- 2003
- Bibcode:
- 2003asdu.confE.177M