The effect of cosmic variance on the characteristics of dust
  polarization power spectra
  In the context of cosmic microwave background polarization studies and the
characterization of the Galactic foregrounds, the power spectrum analysis of
the thermal dust polarization sky has led to intriguing evidence of an E/B
asymmetry and a positive TE correlation. In this work, we produce synthesized
dust polarization maps from a set of global magneto-hydrodynamic (MHD)
simulations of Milky-Way-sized galaxies, and analyze their power spectra at
intermediate angular scales (angular multipoles $\ell \in \left[60 ,\,
140\right]$). We study the role of the initial configuration of the large-scale
magnetic field, its strength, and the feedback on the power spectrum
characteristics. Using full-galaxy MHD simulations, we were able to estimate
the variance induced by the peculiar location of the observer in the galaxy. We
find that the polarization power spectra sensitively depend on the observer's
location, impeding a distinction between different simulation setups. There is
a clear statistical difference between the power spectra measured from within
the spiral arms and those measured from the inter-arm regions. Also, power
spectra from within supernova-driven bubbles share common characteristics,
regardless of the underlying model. However, no correlation was found between
the properties of the polarization power spectra and the local (with respect to
the observer) mean values of physical quantities such as the density and the
strength of the magnetic field. Finally, we find indications that the global
strength of the magnetic field may play a role in shaping the power spectrum
characteristics; as the global magnetic field strength increases, the E/B
asymmetry and the TE correlation increase, whereas the viewpoint-induced
variance decreases. However, we find no direct correlation with the strength of
the local magnetic field that permeates the mapped region of the interstellar
medium.
