In-depth multiscale analysis of polarisation maps
Observations of the polarised dust emission with Planck and the future SPICA at large scale and with ALMA, SCUBA2 and NIKA2 at smaller scales trace the interaction between the magnetic field and the denser part of the ISM as molecular clouds and star formation regions. However, a clear interpretation of the Stokes parameters Q and U, and of the associated polarisation vector P, is difficult. The confusion along the line-of-sight, the mixture between the ordered and turbulent component in the Galaxy and the fluctuations of the polarised signal on a broad range of spatial scales are properties of the magnetic field that makes it hard to interpret.
In this talk, I will present different approaches to analyse and visualise ISM polarisation maps based on multiscale analyses. The first technique called the Multiscale non-Gaussian segmentation (MnGSeg; Robitaille et al. 2014, 2019 to be submitted), was first applied on dust emission and column density maps to locate and extract dense molecular structures and turbulence intermittency. I will show how one can apply this technique on polarisation data to separate the diffuse/“regular” magnetic field fluctuations from singular structures associated with sharp changes of the polarisation angle or intensity. I will also show how this new approach is closely related to the multiscale polarisation gradient technique (Robitaille et al. 2015, 2017) and how both can be used to characterise the Galactic magnetic field and its relation with ISM structures. Both techniques can be applied on the polarised infrared dust emission and the radio synchrotron emission.