Abstract:
Using magnetohydrodynamic simulations of fluctuation dynamos, we perform broad-bandwidth synthetic observations to
investigate the properties of polarized synchrotron emission and the role that Faraday rotation plays in inferring the polarized
structures in the intracluster medium (ICM) of galaxy clusters. In the saturated state of the dynamo, we find a Faraday depth
(FD) dispersion σ FD ≈ 100 rad m−2, in agreement with observed values in the ICM. Remarkably, the FD power spectrum is
qualitatively similar to M(k)/k, where M(k) is the magnetic spectrum and k the wavenumber. However, this similarity is broken
at high k when FD is obtained by applying rotation measure (RM) synthesis to polarized emission from the ICM due to poor
resolution and complexities of spectrum in FD space. Unlike the Gaussian probability distribution function (PDF) obtained for
FD, the PDF of the synchrotron intensity is lognormal. A relatively large σ FD in the ICM gives rise to strong frequency-dependent
variations of the pixel-wise mean and peak polarized intensities at low frequencies ( 1.5 GHz). The mean fractional polarization
p obtained at the resolution of the simulations increases from <0.1 at 0.5 GHz to its intrinsic value of ∼0.3 at 6 GHz. Beam
smoothing significantly affects the polarization properties below 1.5 GHz, reducing p to 0.01 at 0.5 GHz. At frequencies
5 GHz, polarization remains largely unaffected, even when recovered using RM synthesis. Thus, our results underline the
need for high-frequency ( 5 GHz) observations with future radio telescopes to effectively probe the properties of polarized
emission in the ICM.
