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 ($\lesssim 1.5 \, {\rm GHz}$). 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 $\lesssim 1.5\, {\rm GHz}$, reducing 〈p〉 to ≲ 0.01 at 0.5 GHz. At frequencies $\gtrsim 5\, {\rm GHz}$, polarization remains largely unaffected, even when recovered using RM synthesis. Thus, our results underline the need for high-frequency ($\gtrsim 5\, {\rm GHz}$) observations with future radio telescopes to effectively probe the properties of polarized emission in the ICM.

中文翻译：

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波动发电机作用的极化同步加速器发射特性– I.在星系团中的应用

摘要

使用波动动力学的磁流体动力学模拟，我们进行了宽带综合观测，以研究极化同步加速器发射的特性以及法拉第旋转在推断星系团簇内介质（ICM）极化结构中的作用。在上述发电机的饱和状态，我们发现σ法拉第深度（FD）分散_FD ≈100弧度米^-2，与在ICM观测值一致。值得注意的是，FD功率谱在质量上类似于M（k）/ k，其中M（k）是磁谱，k是波数。但是，这种相似性在高k时就被打破了。FD是由于FD空间中较差的分辨率和复杂的光谱，通过对ICM的偏振发射应用旋转测量（RM）合成而获得FD。与通过FD获得的高斯概率分布函数（PDF）不同，同步加速器强度的PDF是对数正态的。相对大的σ _FD在ICM产生了逐像素平均和峰值极化强度的强烈依赖于频率的变化在低频（$ \ lesssim 1.5 \ {\ RM千兆赫} $）。在模拟分辨率下获得的平均分数极化〈p〉从0.5 GHz时的<0.1增加到6 GHz时的〜0.3的固有值。光束平滑会显着影响$ \ lesssim 1.5 \，{\ rm GHz} $以下的偏振特性，从而降低< p〉至0.5 GHz下的≲0.01。在$ \ gtrsim 5 \，{\ rm GHz} $频率下，即使使用RM合成进行恢复，极化也基本上不受影响。因此，我们的结果强调了使用未来的射电望远镜进行高频（$ \ gtrsim 5 \，{\ rm GHz} $）观测的必要性，以有效探测ICM中极化发射的特性。