Polarised radiative transfer, rotation measure fluctuations and large-scale magnetic fields

Abstract

Faraday rotation measure at radio wavelengths is commonly used to diagnose large-scale magnetic fields. It is argued that the length-scales on which magnetic fields vary in large-scale diffuse astrophysical media can be inferred from correlations in the observed RM. RM is a variable which can be derived from the polarised radiative transfer equations in restrictive conditions. This paper assesses the usage of RMF (rotation measure fluctuation) analyses for magnetic field diagnostics in the framework of polarised radiative transfer. We use models of various magnetic field configurations and electron density distributions to show how density fluctuations could affect the correlation length of the magnetic fields inferred from the conventional RMF analyses. We caution against interpretations of RMF analyses when a characteristic density is ill-defined, e.g. in cases of log-normal distributed and fractal-like density structures. As the spatial correlations are generally not the same in the line-of-sight longitudinal direction and the sky plane direction, one also needs to clarify the context of RMF when inferring from observational data. In complex situations, a covariant polarised radiative transfer calculation is essential to capture all aspects of radiative and transport processes, which would otherwise ambiguate the interpretations of magnetism in galaxy clusters and larger-scale cosmological structures.

MNRAS accepted, 18 pages, 9 figures

References in corpus (17)

• The outer scale of turbulence in the magneto-ionized Galactic interstellar medium
• Rotation Measures of Extragalactic Sources Behind the Southern Galactic Plane: New Insights into the Large-Scale Magnetic Field of the Inner Milky Way
• The magnetic field and turbulence of the cosmic web measured using a brilliant fast radio burst
• Buoyancy Instabilities in Weakly Magnetized Low Collisionality Plasmas
• A Global Probe of Cosmic Magnetic Fields to High Redshifts
• Detection of microgauss coherent magnetic fields in a galaxy five billion years ago
• Fluctuation dynamos and their Faraday rotation signatures
• Differences in Faraday Rotation Between Adjacent Extragalactic Radio Sources as a Probe of Cosmic Magnetic Fields
• Faraday conversion and magneto-ionic variations in Fast Radio Bursts
• Conversion Measure of Faraday Rotation-Conversion with application to Fast Radio Bursts
• Redshift evolution of extragalactic rotation measures
• Statistical Techniques for Detecting the Intergalactic Magnetic Field from Large Samples of Extragalactic Faraday Rotation Data
• A compiled catalog of rotation measures of radio point sources
• A Broadband Spectro-polarimetric View of the NVSS Rotation Measure Catalogue I: Breaking the nπ-ambiguity
• Canals in Milky Way radio polarization maps
• Covariant polarized radiative transfer on cosmological scales for investigating large-scale magnetic field structures
• Magnetic fields in nearby galaxies: prospects with future radio telescopes

Cited by in corpus (3)

• Magnetic fields in the Milky Way from pulsar observations: effect of the correlation between thermal electrons and magnetic fields
• Radio Observations as a Probe of Cosmic Web Magnetism
• Spectropolarimetry of synchrotron radiation from relativistic electrons with anisotropic pitch-angle and various energy distributions