Galactic Dust Polarization in Turbulent Multiphase ISM: On the Origin of the EE/BB Asymmetry

Polarized thermal emission from Galactic dust is the dominant foreground for cosmic microwave background polarization measurements at high frequencies, with its statistical properties shaped by the interplay between turbulence and magnetic fields in the multiphase interstellar medium (ISM). Variations in turbulence regime and density–magnetic field alignment across the warm neutral medium (WNM), unstable neutral medium (UNM), and cold neutral medium (CNM) should imprint distinct signatures on the power spectra and EE/BB power ratio, yet the relative contributions of these phases remain poorly constrained. Using high-resolution 3D magnetohydrodynamic simulations of a turbulent multiphase ISM coupled with synthetic dust polarization maps, we quantify phase-dependent turbulence, anisotropy, and alignment properties. We find that the trans-Alfvénic and transonic WNM and UNM are strongly anisotropic, exhibiting tight alignment of density and velocity structures with the local magnetic field. In contrast, the super-Alfvénic and supersonic CNM displays reduced anisotropy and weak alignment. These dynamical differences are reflected in the statistical scaling of fluctuations: the square root of the second-order velocity structure function exhibits a slope near 1/3 in the WNM, near 1/2 in the CNM, and intermediate in the UNM. Comparing our synthetic polarization power spectra with Planck measurements, we find that polarization from UNM dust yields spectral slopes closest to the Planck-inferred values, whereas WNM and CNM dust produces steeper and shallower spectra, respectively. The WNM yields EE / BB > 2, the UNM gives EE / BB ∼ 2, and the CNM yields EE / BB ≈ 1. These results suggest that UNM dust may be an important contributor to the polarized foreground under typical high-latitude ISM conditions. We present predictions at 150 GHz to inform foreground modeling and separation.