Diagnostics of magnetohydrodynamic modes in the ISM through synchrotron polarization statistics
arXiv:2405.17985 · doi:10.3847/1538-4357/ad5af5
Abstract
One of the biggest challenges in understanding Magnetohydrodynamic (MHD) turbulence is identifying the plasma mode components from observational data. Previous studies on synchrotron polarization from the interstellar medium (ISM) suggest that the dominant MHD modes can be identified via statistics of Stokes parameters, which would be crucial for studying various ISM processes such as the scattering and acceleration of cosmic rays, star formation, dynamo. In this paper, we present a numerical study of the Synchrotron Polarization Analysis (SPA) method through systematic investigation of the statistical properties of the Stokes parameters. We derive the theoretical basis for our method from the fundamental statistics of MHD turbulence, recognizing that the projection of the MHD modes allows us to identify the modes dominating the energy fraction from synchrotron observations. Based on the discovery, we revise the SPA method using synthetic synchrotron polarization observations obtained from 3D ideal MHD simulations with a wide range of plasma parameters and driving mechanisms, and present a modified recipe for mode identification. We propose a classification criterion based on a new SPA+ fitting procedure, which allows us to distinguish between Alfvén mode and compressible/slow mode dominated turbulence. We further propose a new method to identify fast modes by analyzing the asymmetry of the SPA+ signature and establish a new asymmetry parameter to detect the presence of fast mode turbulence. Additionally, we confirm through numerical tests that the identification of the compressible and fast modes is not affected by Faraday rotation in both the emitting plasma and the foreground.
18 pages, 10 figures, 1 table, accepted for publication in ApJ
References in corpus (15)
- Theory of Star Formation
- The Athena++ Adaptive Mesh Refinement Framework: Design and Magnetohydrodynamic Solvers
- Cosmic Ray Propagation: Nonlinear Diffusion Parallel and Perpendicular to Mean Magnetic Field
- A Global Probe of Cosmic Magnetic Fields to High Redshifts
- Velocity centroids as tracers of the turbulent velocity statistics
- Tracing interstellar magnetic field using velocity gradient technique: Application to Atomic Hydrogen data
- Polarization of absorption lines as a diagnostics of circumstellar, interstellar and intergalactic magnetic fields: Fine structure atoms
- Study of velocity centroids based on the theory of fluctuations in position-position-velocity space
- Particle Acceleration by Fast Modes in Solar Flares
- Atomic alignment and Diagnostics of Magnetic Fields in Diffuse Media
- Technique for separating velocity and density contributions in spectroscopic data and its application to studying turbulence and magnetic fields
- Polarization from aligned atoms as a diagnostics of circumstellar, AGN and interstellar magnetic fields: II. Atoms with Hyperfine Structure
- Polarimetric studies of magnetic turbulence with interferometer
- Anomalous compressible mode generation by global frame projections of pure Alfven mode
- Magnetic field measurement from the Davis-Chandrasekhar-Fermi method employed with Atomic Alignment