Search for Extreme Rotation Measures in CSS Sources

TL;DR

This study investigates the Faraday rotation in CSS sources using high-frequency VLA observations, revealing large rotation measures indicative of dense magnetized plasma near black holes.

Contribution

It provides new measurements of Faraday rotation measures in CSS sources at high frequencies, expanding understanding of magnetic environments close to AGN black holes.

Findings

Detected large rotation measures in CSS sources

Observed frequency-dependent polarization rotation

Confirmed dense magnetized plasma near black holes

Abstract

Magnetized plasmas traversed by linearly polarized light will reveal their presence by the frequency dependent Faraday rotation of the angle of polarization. The regions surrounding the black holes powering the jets in AGNs are expected to have dense magnetized plasmas, possibly giving rise to very large Faraday rotations. Compact steep spectrum (CSS) sources are good candidates to search for very large Faraday rotated components as they contain compact emission from close to the black hole and many are strongly depolarized at centimeter wavelengths as expected from strong Faraday effects. We present data on several CSS sources (3C48, 3C138 and 3C147) observed with the VLA at frequencies between 20 and 48 GHz in the most extended configuration. Large, but not excessive rotation measures are reported.