Speaker
Description
Observations of diffuse interstellar polarization at meter wavelengths reveal intricate Faraday depth structures, likely tracing interactions between magnetized plasma and neutral gas. A strong correlation with CNM filaments has been proposed, but not reproduced in simulations with low CNM fractions, suggesting the CNM content may shape Faraday structures.
We investigate whether the CNM fraction drives the correlation between Faraday structures and HI brightness temperature, as observed in the 3C196 field. Using numerical simulations with varying CNM content, we test the role of cold gas in coupling neutral structures to magnetized plasma, and assess the influence of turbulence and magnetic field topology.
We analyze 14 three-dimensional magnetohydrodynamic (MHD) simulations of Fourier-driven turbulence in 50 pc cubes, post-processed with the MOOSE code to generate synthetic synchrotron polarization and Faraday tomography. We compute spatial correlations between Faraday depth structures and phase-separated HI brightness temperature using the Histogram of Oriented Gradients (HOG) method and compare results with LOFAR observations, including instrumental effects.
The correlation strength depends primarily on magnetic field orientation and turbulence, not solely on CNM abundance. When the mean field is aligned with the line of sight, the WNM dominates the correlation, even at high CNM fractions. In the perpendicular case, the correlation weakens for all phases. Noise affects the phases differently and modulates the correlation amplitude.
None of the simulations fully reproduces the observed dominance of CNM in 3C196.
Our results show that CNM fraction alone is insufficient to explain the correlation with Faraday structures. Turbulence,
magnetic field dynamics, and topology are also key factors, highlighting the need for a comprehensive approach to understanding the
coupling between neutral gas and magnetized plasma in the diffuse ISM.
