Intermittency in the Multiphase ISM --- II. Non-Gaussian Dust Polarization and Foreground Variance

Abstract

Interstellar turbulence produces non-Gaussian polarized Galactic dust emission whose higher-order statistics depend on thermal phase and turbulent forcing. We synthesize optically thin dust polarization from three thermally multiphase diffuse interstellar medium (ISM) simulations with compressive, mixed, and solenoidal forcing. We characterize the resulting non-Gaussian structure in the warm, unstable, and cold phases using $E$- and $B$-mode spectra, one-point distributions, scale-dependent increments, and Minkowski functionals. Both $E$ and $B$ modes are intermittent. Warm-phase emission remains closest to Gaussian, whereas cold gas shows flatter intermediate-scale spectra, broader non-Gaussian tails, and the strongest departures from Gaussian morphology. Compressive forcing generally produces the strongest projected intermittency, particularly in the cold phase and total emission, while mixed and solenoidal forcing show weaker signatures. These higher-order structures also enhance spatial fluctuations in polarized dust power: Gaussian fields matched to the same two-point covariance underestimate the region-to-region scatter by factors of up to $\sim2.6$. Our results show that thermal phase and turbulent forcing regulate not only the mean polarized dust spectrum but also the field-to-field distribution of foreground power, with implications for modeling Galactic foreground in CMB polarization measurements.