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arXiv · astro-ph/0611374

Spectropolarimetry of the 3.4 micron absorption feature in NGC 1068

R. E. Mason·G. S. Wright·A. Adamson·Y. Pendleton
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Abstract

In order to test the silicate-core/organic-mantle model of galactic interstellar dust, we have performed spectropolarimetry of the 3.4 micron C-H bond stretch that is characteristic of aliphatic hydrocarbons, using the nucleus of the Seyfert 2 galaxy, NGC 1068, as a bright, dusty background source. Polarization calculations show that, if the grains in NGC 1068 had the properties assigned by the core-mantle model to dust in the galactic diffuse ISM, they would cause a detectable rise in polarization over the 3.4 micron feature. No such increase is observed. We discuss modifications to the basic core-mantle model, such as changes in grain size or the existence of additional non-hydrocarbon aligned grain populations, which could better fit the observational evidence. However, we emphasize that the absence of polarization over the 3.4 micron band in NGC 1068 - and, indeed, in every line of sight examined to date - can be readily explained by a population of small, unaligned carbonaceous grains with no physical connection to the silicates.

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R. E. Mason, G. S. Wright, A. Adamson, Y. Pendleton. 2006-11-13. Spectropolarimetry of the 3.4 micron absorption feature in NGC 1068. https://doi.org/10.1086/510608

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