Line Polarization of Molecular Lines at Radio Frequencies: The Case of DR 21(OH)
Line Polarization of Molecular Lines at Radio Frequencies: The Case of DR 21(OH)
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射频下分子线的线偏振：DR 21(OH) 的案例
DOI：
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发表时间：
2005
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通讯作者：
W. D. Watson
中科院分区：
文献类型：
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作者：
P. Cortés;R. Crutcher;W. D. Watson
本文报道了DR 21（OH）中3mm热尘埃辐射和CO J = 1 → 0谱线辐射的偏振观测结果。观测结果是使用伯克利-伊利诺伊-马里兰州协会（比马）阵列获得的。Lai等人在1.3 mm处观察到了该区域的偏振连续发射，并测量了CO J = 2 → 1偏振。我们的连续极化结果与Lai等人的结果一致，但J = 1 → 0的线极化方向与CO J = 2 → 1的线极化方向垂直.这个意想不到的结果进行了探索，通过获得数值解的多层辐射传输方程的气体各向异性的光学深度。我们发现，除了各向异性的光学深度，各向异性的激发，由于外部的CO的辐射源是需要了解的正交性的偏振方向。DR 21（OH）核心的尘埃颗粒的连续辐射足以提供这种外部辐射。CO极化必须出现在相对低密度（n~100 cm-3）的包层气体中。我们推断在这种气体中B~10 μ G，这意味着包线是亚临界的。
We present polarization observations in DR 21(OH) from thermal dust emission at 3 mm and from CO J = 1 → 0 line emission. The observations were obtained using the Berkeley-Illinois-Maryland Association (BIMA) array. Lai et al. observed this region at 1.3 mm for the polarized continuum emission and also measured the CO J = 2 → 1 polarization. Our continuum polarization results are consistent with those of Lai et al. However, the direction of the linear polarization for the J = 1 → 0 is perpendicular to that of the CO J = 2 → 1 polarization. This unexpected result was explored by obtaining numerical solutions to the multilevel radiative transfer equations for a gas with anisotropic optical depths. We find that in addition to the anisotropic optical depths, anisotropic excitation due to a source of radiation that is external to the CO is needed to understand the orthogonality in the directions of polarization. The continuum emission by dust grains at the core of DR 21(OH) is sufficient to provide this external radiation. The CO polarization must arise in relatively low density (n ~ 100 cm-3 ) envelope gas. We infer B ~ 10 μG in this gas, which implies that the envelope is subcritical.