The Dielectric Function of "Astrodust" and Predictions for Polarization in the 3.4$\mu$m and 10$\mu$m Features

Understand

The dielectric function of interstellar dust material is modeled using observations of extinction and polarization in the infrared, together with estimates for the mass of interstellar dust.

• The "astrodust" material is assumed to be a mix of amorphous silicates and other materials, including hydrocarbons producing an absorption feature at 3.4$\mu$m.
• The detailed shape of the 10$\mu$m polarization profile depends on the assumed porosity and grain shape, but the 10$\mu$m spectropolarimetric data are not yet good enough to clearly favor one shape over another, nor to constrain the porosity.
• The expected 3.4$\mu$m feature polarization is consistent with existing upper limits, provided the 3.4$\mu$m absorption is preferentially located in grain surface layers; a separate population of non-aligned carbonaceous grains is not required.