Radio sources with ultra-high polarization

TL;DR

This study identifies 129 radio sources with ultra-high linear polarization, revealing that their high polarization is likely due to intrinsic magnetic field properties rather than environmental factors.

Contribution

The paper presents a new sample of highly polarized radio sources and investigates their properties, concluding intrinsic magnetic field characteristics cause their extreme polarization.

Findings

Sources are mostly elliptical galaxies with typical AGN features.

Environmental analysis shows no significant difference from low-polarization sources.

High polarization likely due to intrinsic magnetic field properties.

Abstract

A sample of 129 unresolved radio sources with ultrahigh linear polarization (>30 per cent) has been selected from the NRAO VLA Sky Survey. Such high average linear polarization is unusual in extragalactic sources. Higher resolution Australia Telescope Compact Array and Very Large Array observations confirm the high average polarization but find that most of these sources are extended. The Sloan Digital Sky Survey spectroscopy, where available, shows that the optical counterparts are elliptical galaxies with no detectable emission lines. The optical spectra, radio luminosity, linear size and spectral index of these sources are typical of radio-loud active galactic nuclei. Galaxy counts within a 1 Mpc radius of the radio sources show that these highly polarized sources are in environments similar to their low polarization (<2 per cent) counterparts. Similarly, the line-of-sight environments of the ultrahigh polarization sources are on average indistinguishable from those of the low-polarization sources. We conclude that the extraordinarily high average polarization must be due to intrinsic properties of the sources, such as an extremely ordered source magnetic field, low internal thermal plasma density or a preferential orientation of the source magnetic field perpendicular to the line of sight.