A new perspective on turbulent Galactic magnetic fields through comparison of linear polarisation decomposition techniques

Abstract

We compare two rotationally invariant decomposition techniques on linear polarisation data: the spin-2 spherical harmonic decomposition in two opposite parities, the $E$- and $B$-mode, and the multiscale analysis of the gradient of linear polarisation, $|\nabla \mathbf{P}|$. We demonstrate that both decompositions have similar properties in the image domain and the spatial frequency domain. They can be used as complementary tools for turbulence analysis of interstellar magnetic fields in order to develop a better understanding of the origin of energy sources for the turbulence, the origin of peculiar magnetic field structures and their underlying physics. We also introduce a new quantity $|\nabla EB|$ based on the $E$- and $B$-modes and we show that in the intermediate and small scales limit $|\nabla EB|\simeq |\nabla \mathbf{P}|$. Analysis of the 2.3 GHz S-band Polarization All Sky Survey (S -PASS) shows many extended coherent filament-like features appearing as 'double-jumps' in the $|\nabla \mathbf{P}|$ map that are correlated with negative and positive filaments of $B$-type polarisation. These local asymmetries between the two polarisation types, $E$ and $B$, of the non-thermal Galactic synchrotron emission have an influence on the $E$- and $B$-mode power spectra analyses. The wavelet-based formalism of the polarisation gradient analysis allows us to locate the position of $E$- or $B$-mode features responsible for the local asymmetries between the two polarisation types. In analysed subregions, the perturbations of the magnetic field are trigged by star clusters associated with HII regions, the Orion-Eridanus superbubble and the North Polar Spur at low Galactic latitude.

Accepted for publication on MNRAS (2017 March 10), 20 pages, 14 figures

References in corpus (15)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Giant Magnetized Outflows from the Centre of the Milky Way
• A New Model For The Loop-I (The North Polar Spur) Region
• The Southern Galactic Plane Survey: Polarized Radio Continuum Observations and Analysis
• How to De-Rotate the Cosmic Microwave Background Polarization
• Polarised radio filaments outside the Galactic plane
• Herschel's view of the large-scale structure in the Chamaeleon dark clouds
• Structure analysis of interstellar clouds: I. Improving the Delta-variance method
• A radio-polarisation and rotation measure study of the Gum Nebula and its environment
• Galactic interstellar turbulence in the southern sky seen through spatial gradients of the polarization vector
• Characterising Complexity in Solar Magnetogram Data using a Wavelet-based Segmentation Method
• Structure analysis of interstellar clouds: II. Applying the Delta-variance method to interstellar turbulence
• Second-Generation Curvelets on the Sphere
• Directional spin wavelets on the sphere
• GALFACTS: The G-ALFA Continuum Transit Survey

Cited by in corpus (11)

• S-band Polarization All Sky Survey (S-PASS): survey description and maps
• The magnetic environment of the Orion-Eridanus superbubble as revealed by Planck
• Through thick or thin: Multiple components of the magneto-ionic medium towards the nearby $\mathrm{H}\mathrm{II}$ region Sharpless 2-27 revealed by Faraday tomography
• The Simons Observatory: Galactic Science Goals and Forecasts
• Is there a left-handed magnetic field in the solar neighborhood? Exploring helical magnetic fields in the interstellar medium through dust polarization power spectra
• Advanced Diagnostics for the Study of Linearly Polarized Emission. I: Derivation
• Decomposing Magnetic Fields in Three Dimensions over the Central Molecular Zone
• A comparison between Faraday Tomography and Synchrotron Polarization Gradients
• Interstellar magnetic cannon targeting the Galactic halo : A young bubble at the origin of the Ophiuchus and Lupus molecular complexes
• Turbulent magnetic field in the HII region Sh 2-27
• The Galactic latitude dependency of Faraday complexity in the S-PASS/ATCA RM catalogue