The question of extinction in active galactic nuclei: Infrared spectral observations of NGC 1614, NGC 7469 and NGC 1275

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Abstract
Summary. We present 8–3 µm spectra of the nuclei of the three active galaxies NGC 1614, 7469 and 1275. For the first time the [Ne II] fine structure line and the unidentified ‘11.25 µm’ feature are definitively observed in a Seyfert nucleus, NGC 7469, and are also seen in the high luminosity emission-line nucleus of NGC 1614. It is shown that the observations are consistent with there being no large optical extinction of amount AV ≳ 10 mag in any of these objects. It is argued that the observation of the 11.25 or 8.65 µm emission features makes suspect any quantative estimates of extinction based on the depth of the 10 µm minimum. However, the presence of such resolved features in the type 1 Seyfert NGC 7469 and in NGC 1614 indicates a dust-emission mechanism, whereas the featureless spectrum of NGC 1275 shows no evidence for the presence of dust in this object.

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