普朗克中间结果。XLIV。从南银河帽尘埃极化图看银河磁场的结构
Planck intermediate results. XLIV. The structure of the Galactic magnetic field from dust polarization maps of the southern Galactic cap
摘要：
利用353 GHz的Stokes参数Planck图，研究了银河系高纬度星际尘埃偏振的统计特性。我们的目标是推进对磁化星际介质（ISM）的理解，并为宇宙微波背景成分分离程序提供一个偏振尘埃前景模型。聚焦于南银河帽，我们研究的统计分布的极化分数（$p$）和角度（$ψ$）的特点的有序和湍流的银河磁场（GMF）的组件在太阳附近。我们在大角度尺度上的偏振模式的平均（有序）GMF朝向银河系坐标$(l_0,b_0)=(70^\circ \pm 5^\circ,24^\circ \pm 5^\circ)$的方向。$p$的直方图显示了高达25%的宽分散。$ψ$的直方图具有关于从有序GMF期望的规则图案的$12^\circ$的标准偏差。我们使用这些直方图来建立一个现象学模型的湍流成分的GMF，假设一个统一的有效偏振分数（$p_0$）的灰尘排放。为了模拟斯托克斯参数，我们近似的积分沿视线（LOS）作为一组$N$独立的偏振层，在每个层中的湍流分量的GMF从高斯实现的幂律功率谱的总和。我们能够重现所观察到的$p$和$ψ$的分布使用：（26 $\pm$ 3）%的$p_0$值; 0.9 $\pm$ 0.1之间的湍流和GMF的平均分量的强度的比率;和一个小的值$N$。我们与极化层的密度结构和相关长度的GMF沿LOS。
英文摘要：
We study the statistical properties of interstellar dust polarization at high Galactic latitude, using the Stokes parameter Planck maps at 353 GHz. Our aim is to advance the understanding of the magnetized interstellar medium (ISM), and to provide a model of the polarized dust foreground for cosmic microwave background component-separation procedures. Focusing on the southern Galactic cap, we examine the statistical distributions of the polarization fraction ($p$) and angle ($ψ$) to characterize the ordered and turbulent components of the Galactic magnetic field (GMF) in the solar neighbourhood. We relate patterns at large angular scales in polarization to the orientation of the mean (ordered) GMF towards Galactic coordinates $(l_0,b_0)=(70^\circ \pm 5^\circ,24^\circ \pm 5^\circ)$. The histogram of $p$ shows a wide dispersion up to 25 %. The histogram of $ψ$ has a standard deviation of $12^\circ$ about the regular pattern expected from the ordered GMF. We use these histograms to build a phenomenological model of the turbulent component of the GMF, assuming a uniform effective polarization fraction ($p_0$) of dust emission. To model the Stokes parameters, we approximate the integration along the line of sight (LOS) as a sum over a set of $N$ independent polarization layers, in each of which the turbulent component of the GMF is obtained from Gaussian realizations of a power-law power spectrum. We are able to reproduce the observed $p$ and $ψ$ distributions using: a $p_0$ value of (26 $\pm$ 3)%; a ratio of 0.9 $\pm$ 0.1 between the strengths of the turbulent and mean components of the GMF; and a small value of $N$. We relate the polarization layers to the density structure and to the correlation length of the GMF along the LOS.
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