Planck dust polarization power spectra are consistent with strongly supersonic turbulence
arxiv(2024)
Abstract
The polarization of the Cosmic Microwave Background (CMB) is rich in
information but obscured by foreground emission from the Milky Way's
interstellar medium (ISM). To uncover relationships between the underlying
turbulent ISM and the foreground power spectra, we simulated a suite of driven,
magnetized, turbulent models of the ISM, varying the fluid properties via the
sonic Mach number, Ms, and magnetic (Alfv\'en) Mach number, Ma. We measure the
power spectra of density ($\rho$), velocity ($v$), magnetic field ($H$), total
projected intensity ($T$), parity-even polarization ($E$), and parity-odd
polarization ($B$). We find that the slopes of all six quantities increase with
Ms and tend to increase with Ma. By comparing spectral slopes of $E$ and $B$ to
those measured by Planck, we infer typical values of Ms and Ma for the ISM. As
the fluid velocity increases, the ratio of BB power to EE power increases to
approach a constant value near the Planck-observed value of $\sim 0.5$ for $Ms
> 4$, regardless of the magnetic field strength. We also examine
correlation-coefficients between projected quantities, and find that
$r^{TE}\approx 0.3$, in agreement with Planck, for appropriate combinations of
Ms and Ma. {Finally, we consider parity-violating correlations $r^{TB}$ and
$r^{EB}$
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