射电星系3C 120喷流中法拉第旋转的来源
On the source of Faraday rotation in the jet of the radio galaxy 3C120
摘要：
通过1999年至2007年在86、43、22、15、12、8、5、2和1.7 GHz进行的甚长基线阵列观测，分析了射电星系3C 120喷流中法拉第旋转的来源。对1999年至2001年的观测结果进行比较，揭示了底层喷流发射和法拉第旋转屏的线性偏振的不相关变化：而旋转量度（RM）在距核心大约2和5质量之间保持恒定，RM校正的电矢量位置角（EVPA）两个超光速组件的旋转几乎90度时，与其他组件移动通过类似的喷流位置相比。另一方面，最里面的2个mas经历了RM的显著变化-包括符号反转-但在RM校正的EVPA中没有变化。同样，2007年的观测结果显示，沿喷流的RM出现了双符号反转，而RM校正的EVPA仍然垂直于喷流轴。虽然所观察到的相干结构和梯度的RM沿射流支持的想法，即法拉第旋转是由周围的发射射流的热电子鞘产生的，在RM和RM校正EVPA的不相关的变化表明，发射射流和法拉第旋转的源物理上并不紧密相连，并具有不同的配置的磁场和/或运动学性质。此外，存在一个区域的增强RM的属性保持不变，超过三年需要一个本地化的法拉第旋转源，有利于一个模型，其中一个显着的一部分RM起源于前景云。
英文摘要：
The source of Faraday rotation in the jet of the radio galaxy 3C120 is analyzed through Very Long Baseline Array observations carried out between 1999 and 2007 at 86, 43, 22, 15, 12, 8, 5, 2, and 1.7 GHz. Comparison of observations from 1999 to 2001 reveals uncorrelated changes in the linear polarization of the underlying jet emission and the Faraday rotation screen: while the rotation measure (RM) remains constant between approximately 2 and 5 mas from the core, the RM-corrected electric vector position angles (EVPAs) of two superluminal components are rotated by almost 90 degrees when compared to other components moving through similar jet locations. On the other hand, the innermost 2 mas experiences a significant change in RM -- including a sign reversal -- but without variations in the RM-corrected EVPAs. Similarly, observations in 2007 reveal a double sign reversal in RM along the jet, while the RM-corrected EVPAs remain perpendicular to the jet axis. Although the observed coherent structure and gradient of the RM along the jet supports the idea that the Faraday rotation is produced by a sheath of thermal electrons that surrounds the emitting jet, the uncorrelated changes in the RM and RM-corrected EVPAs indicate that the emitting jet and the source of Faraday rotation are not closely connected physically and have different configurations for the magnetic field and/or kinematical properties. Furthermore, the existence of a region of enhanced RM whose properties remain constant over three years requires a localized source of Faraday rotation, favoring a model in which a significant fraction of the RM originates in foreground clouds.
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