Rotation measure synthesis at the 2 m wavelength of the FAN region: unveiling screens and bubbles
Rotation measure synthesis at the 2 m wavelength of the FAN region: unveiling screens and bubbles
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FAN 区域 2 m 波长处的旋转测量合成：揭开屏幕和气泡
DOI：
10.1051/0004-6361/201220175
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发表时间：
2012
影响因子：
6.5
通讯作者：
R. Nijmegen
中科院分区：
文献类型：
--
作者：
M. Iacobelli;M. Haverkorn;Peter Katgert Leiden University;Astron;The Netherlands Institute for Radio Astronomy;R. Nijmegen
上下文。韦斯特堡综合射电望远镜在L=137deg，b=+7deg的扇区2m处的旋转测量合成显示了星际电离介质中结构的形态。λ=137deg，b=+7。
目的：我们从星际介质中的相干结构和星际磁场的性质来解释漫射极化同步辐射。
方法：对旋转测量合成得到的偏振数据立方体进行统计分析。首次将互相关用于识别和表征法拉第深度空间中的极化结构。有关该介质的补充信息来自H{$α$}发射、附近脉冲星的性质和光学偏振星光测量。
结果：在[-13，+5]radm-2}$的法拉第深度范围内，我们发现了一个总体不对称的Faraday色散函数，该函数在-1radm$^-2}$附近达到峰值。识别出三种形态模式，显示了从度数到光束大小的结构。第一个结构是附近的一个法拉第深度较低的同步辐射组件，填满了整个视场。第二种模式是具有增强(负)法拉第深度的圆极化结构，其具有与第三组分内的低发射区相同的形态。这第三个分量被解释为其中嵌入圆形结构的背景。在较低的法拉第深度值下，在成像场上检测到一个低梯度，几乎与银河系平面对齐。法拉第深度空间极化结构的功率谱提供了湍流的证据。
结论：法拉第深度从近分量到圆形分量的符号反转表示磁场分量沿视线方向的反转，在很远的距离内从靠近观察者到远离观察者。到附近延伸组件的距离估计为{lsim}100 pC，这表明该结构对应于局部气泡壁。对于圆形分量，讨论了各种物理解释。最可能的解释是，圆形成分似乎是附近(约200 pC外)的斯特龙格伦残骸球体的存在，与一颗古老的不明白矮星有关，并在低密度环境中膨胀。法拉第旋转数据立方体仅在CDS通过匿名ftp到cdsarc.u-strasbg.fr(130.79.128.5)或通过http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A56获得
Context. Rotation measure synthesis of the Westerbork Synthesis Radio Telescope (WSRT) observations at {$λ$} ~{} 2 m of the FAN region at l = 137{deg}, b = +7{deg} shows the morphology of structures in the ionized interstellar medium.
Aims: We interpret the diffuse polarized synchrotron emission in terms of coherent structures in the interstellar medium and the properties of the interstellar magnetic field.
Methods: We performed statistical analysis of the polarization data cube obtained through rotation measure synthesis. For the first time, cross-correlation is applied to identify and characterize polarized structures in Faraday depth space. Complementary information about the medium are derived from H{$α$} emission, properties of nearby pulsars, and optical polarized starlight measurements.
Results: We find an overall asymmetric Faraday dispersion function in a Faraday depth range of [-13, +5] rad m$^{-2}$, which is peaked around -1 rad m$^{-2}$. Three morphological patterns are recognized, showing structures on scales from degrees down to the beam size. The first structure is a nearby synchrotron emission component with low Faraday depth, filling the entire field of view. The second pattern is a circular polarization structure with enhanced (negative) Faraday depth, which has the same morphology as a low-emission region within the third component. This third component is interpreted as the background in which the circular structure is embedded. At low Faraday depth values, a low gradient across the imaged field is detected, almost aligned with the Galactic plane. Power spectra of polarized structures in Faraday depth space provide evidence of turbulence.
Conclusions: A sign reversal in Faraday depth from the nearby component to the circular component indicates a reversal of the magnetic field component along the line of sight, from towards the observer and nearby to away from the observer at large distances. The distance to the nearby, extended component is estimated as {lsim}100 pc, which suggests that this structure corresponds to the Local Bubble wall. For the circular component, various physical interpretations are discussed. The most likely explanation is that the circular component seems to be the presence of a nearby (~{}200 pc away) relic Stromgren sphere, associated with an old unidentified white dwarf star and expanding in a low-density environment. Faraday rotation datacubes are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A56