Spatial Variations of the Interstellar Polarization and Interstellar Extinction

TL;DR

This study compares interstellar polarization and extinction for over 5000 stars, revealing spatial variations and their relation to local structures like the Local Bubble and spiral arms, using Gaia and Hipparcos data.

Contribution

It provides the largest comparison of polarization and extinction using Gaia TGAS parallaxes, revealing spatial patterns and dust properties in the local interstellar medium.

Findings

Polarization and extinction are negligible inside 80 pc from the Sun.

Rapid growth of polarization and extinction occurs in the Local Bubble shell at 80-118 pc.

Polarization efficiency is lower in the Gould belt dust layer compared to the equatorial dust layer.

Abstract

For more than 5000 stars with accurate parallaxes from the Hipparcos and Gaia DR1 Tycho-Gaia astrometric solution (TGAS), Tycho-2 photometry, interstellar polarization from eight catalogues and interstellar extinction from eight 3D maps the largest up to date comparison of the polarization and extinction is provided. The extinction maps give different estimations of the extinction and of the polarization efficiency as the polarization divided into extinction $P/A_V$ as well as of the percentage of the stars with the polarization efficiency higher than the limit of Serkowski $P/A_V>0.03$. Using the Hipparcos parallaxes we found about 200 stars (4\%, mainly OB stars) drop higher than the limit when we use any extinction map. However, the usage of more accurate TGAS parallaxes decreases them to only 17 stars (0.3\%). The polarization and extinction are negligible inside the Local Bubble within 80 pc from the Sun. In the vast Bubble's shell at the distances 80--118 pc from the Sun the polarization and extinction rapidly grow with the distance whereas the position angle of the polarization is oriented predominantly along the shell of the Bubble. Outside the Bubble the polarization and extinction grow with the distance slowly. In addition, within a radius of 80--300 pc of the Sun a disc of some filamentary dust clouds (including well-known Markkanen cloud) is observed as in the polarization map as in the reddening one by Schlegel et al. In this disc the position angle of polarization is preferably oriented along the plane of the disk. For the regions further than 300 pc the position angle of polarization is preferably oriented along the Local spiral arm, i.e. Y coordinate axis. The polarization and its efficiency is lower in the dust layer in the Gould belt than in the equatorial dust layer. It may means different properties of dust in these two layers.