Investigating the effects of finite resolution on observed transverse Rotation Measure distributions

TL;DR

This paper investigates how finite resolution in radio observations affects the detection and interpretation of transverse Faraday Rotation Measure structures in AGN jets, using simulations to assess resolution requirements.

Contribution

It provides a systematic analysis of the impact of finite resolution on observed transverse RM structures through simulated imaging, informing observational strategies.

Findings

Finite resolution blurs transverse RM structures.

Resolution must be sufficiently high to detect systematic RM gradients.

Simulations help determine resolution thresholds for reliable measurements.

Abstract

Both the emission properties and evolution of Active Galactic Nuclei (AGN) radio jets are dependent on the magnetic (B) fields that thread them. Faraday Rotation measurements are a very important way of investigating these B fields, and can provide information on the orientation and structure of the B field in the immediate vicinity of the jet; for example, a toroidal or helical B field component should give rise to a systematic gradient in the observed Faraday rotation across the jet, as well as characteristic intensity and polarization profiles. However, real observed radio images have finite resolution, usually expressed via convolution with a Gaussian beam whose size corresponds to the central lobe of the point source response function. This will tend to blur the transverse structure of the jet, raising the question of how well resolved a jet must be in the transverse direction in order to reliably detect transverse structure. We present the results of simulated Faraday rotation images designed to directly investigate the effect of finite resolution on observed transverse Faraday rotation measure structures.