高红移GPS类星体OQ172的多频VLBA偏振测量
Multi-frequency VLBA Polarimetry of the high-redshift GPS Quasar OQ172
摘要：
2005年，利用甚长基线阵列（VLBA）偏振测量技术，在1.6，2.2，4.8，8.3和15.3GHz对GHZ峰谱类星体OQ172（J1445 + 0958）进行了多频观测。核心喷流结构中检测到的所有带与射流强烈弯曲约3质量从核心。源的无线电发射在所有五个波段都是偏振的。我们研究了在所有五个波段的核心和喷流组件的法拉第旋转，并发现在4.8和8.3 GHz的核心和喷流组件的法拉第旋转良好的线性拟合。在这两个频率下，旋转测量（RM）在核心中为$\sim 2000~\rm rad~m^{-2}$，在内部射流部件中为$\sim 700~\rm rad~m^{-2}$，并且在外部射流部分处继续减小。我们发现，在4.8和8.3 GHz的去极化可能是由源中的内部介质。本文研究了VLBI各分量转换谱与同步辐射自吸收（SSA）和自由-自由吸收（FFA）模型的一致性。虽然这两个模型不能很容易地区分，由于缺乏低频数据，物理参数可以约束每个模型。我们发现，大宽度的$\rm [OIII]_{5007}$线可能是由射流与窄线区（NLR）介质的相互作用。射流弯曲，显着的RM变化，法拉第去极化，光谱周转，和宽线宽的$\rm [OIII]_{5007}$可能是密切相关的，可能是由相同的核介质，大概NLR。
英文摘要：
Multi-frequency Very Long Baseline Array (VLBA) polarimetry observation of the GHz-Peaked Spectrum (GPS) quasar OQ172 (J1445+0958) has been performed at 1.6, 2.2, 4.8, 8.3 and 15.3 GHz in 2005. Core-jet structures are detected in all bands with the jet strongly bent at about 3 mas from the core. The radio emission of the source is polarised at all five bands. We study the Faraday Rotation in the core and jet components at all five bands, and find good linear fits of Faraday Rotation in the core and jet components at 4.8 and 8.3 GHz. At these two frequencies, the Rotation Measure (RM) is $\sim 2000~\rm rad~m^{-2}$ in the core and $\sim 700~\rm rad~m^{-2}$ in the inner jet components and continues to decrease at the outer jet parts. We find that the depolarisation at 4.8 and 8.3 GHz might be caused by the internal medium in the source. We investigate consistency of the turnover spectra of VLBI components with the Synchrotron Self-Absorption (SSA) and Free-Free Absorption (FFA) models. Although these two models can not be easily distinguished due to the lack of low-frequency data, the physical parameters can be constrained for each model. We find that the large width of the $\rm [OIII]_{5007}$ line is likely caused by a jet interaction with a Narrow Line Region (NLR) medium. The jet bending, significant RM variations, Faraday depolarisation, spectral turnover, and broad line width of $\rm [OIII]_{5007}$ could be closely related, likely caused by the same nucleus medium, presumably NLR.
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