Interstellar polarization and grain alignment: the role of iron and silicon

TL;DR

This study investigates how the composition of interstellar dust, specifically iron and silicon, influences polarization, revealing that silicate grains aligned by radiation are primarily responsible for observed polarization.

Contribution

It provides the first detailed correlation analysis between dust grain composition and interstellar polarization, emphasizing the role of silicate grains in polarization mechanisms.

Findings

Anticorrelation between polarization and iron abundance in non-silicate grains.

Correlation between polarization and silicon abundance.

No correlation between polarization efficiency and dust composition.

Abstract

We compiled the polarimetric data for a sample of lines of sight with known abundances of Mg, Si, and Fe. We correlated the degree of interstellar polarization $P$ and polarization efficiency (the ratio of $P$ to the colour excess $E(B-V)$ or extinction $A_V$) with dust phase abundances. We detect an anticorrelation between $P$ and the dust phase abundance of iron in non silicate - containing grains $< [\rm Fe(rest)/H > ]_\rm d$, a correlation between $P$ and the abundance of Si, and no correlation between $P/E(B-V)$ or $P/A_V$ and dust phase abundances. These findings can be explained if mainly the silicate grains aligned by the radiative mechanism are responsible for the observed interstellar linear polarization.