Integrated Optical Polarization of Nearby Galaxies

TL;DR

This study presents the largest optical polarization survey of 70 nearby galaxies, revealing that most have low polarization levels and that dust scattering influences their polarization properties, especially in unbarred spirals.

Contribution

It provides new large-scale observational data on galaxy polarization and confirms the dust scattering model's predictions for unbarred spiral galaxies.

Findings

Most galaxies have polarization <1%.

Dust scattering is the main polarization source.

Unbarred spirals follow the sin^2i inclination relation.

Abstract

We performed an integrated optical polarization survey of 70 nearby galaxies to study the relationship between linear polarization and galaxy properties. To date this is the largest survey of its kind. The data were collected at McDonald Observatory using the Imaging Grism Polarimeter on the Otto Struve 2.1m telescope. Most of the galaxies did not have significant level of linear polarization, where the bulk is <1%. A fraction of the galaxies showed a loose correlation between the polarization and position angle of the galaxy, indicating that dust scattering is the main source of optical polarization. The unbarred spiral galaxies are consistent with the predicted relationship with inclination from scattering models of ~sin^2i.