Abstract
Dust emission is the main foreground for cosmic microwave background polarization. Its statistical characterization must be derived from the analysis of observational data because the precision required for a reliable component separation is far greater than what is currently achievable with physical models of the turbulent magnetized interstellar medium. This Letter takes a significant step toward this goal by proposing a method that retrieves non-Gaussian statistical characteristics of dust emission from noisy Planck polarization observations at 353 GHz. We devised a statistical denoising method based on wavelet phase harmonics (WPH) statistics, which characterize the coherent structures in non-Gaussian random fields and define a generative model of the data. The method was validated on mock data combining a dust map from a magnetohydrodynamic simulation and Planck noise maps. The denoised map reproduces the true power spectrum down to scales where the noise power is an order of magnitude larger than that of the signal. It remains highly correlated to the true emission and retrieves some of its non-Gaussian properties. Applied to Planck data, the method provides a new approach to building a generative model of dust polarization that will characterize the full complexity of the dust emission. We also release PyWPH, a public Python package, to perform GPU-accelerated WPH analyses on images.
Highlights
The quest of primordial B-modes in the polarization of the cosmic microwave background (CMB) faces a major challenge, namely the accurate characterization of one of its main foregrounds: the polarized emission of interstellar dust from our Galaxy (BICEP2/Keck and Planck Collaborations 2015)
The Galactic contribution is sourced by the thermal emission of nonspherical dust grains in the diffuse interstellar medium (ISM)
We introduce a statistical denoising method using the wavelet phase harmonics (WPH) statistics to retrieve the statistical properties of the noise-free dust emission
Summary
The quest of primordial B-modes in the polarization of the cosmic microwave background (CMB) faces a major challenge, namely the accurate characterization of one of its main foregrounds: the polarized emission of interstellar dust from our Galaxy (BICEP2/Keck and Planck Collaborations 2015). The statistical characterization of Galactic polarized foregrounds is important to extract the CMB lensing potential from sky observations (Beck et al 2020). The Galactic contribution is sourced by the thermal emission of nonspherical dust grains in the diffuse interstellar medium (ISM). The mixture of dust and gas is described as a turbulent magnetized fluid, and the grains tend to align statistically with their long axes perpendicular to the local magnetic field, polarizing the emission (Planck Collaboration XII 2020). The physical and chemical processes regulating and structuring the diffuse ISM are nonlinearly coupled (Draine 2011), leading to the emergence of strong scale couplings, which may be evidenced by the highly non-Gaussian statistics observed for many tracers (Burkhart et al 2009)
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