TW Hya盘中分子线极化的发现
Discovery of Molecular Line Polarization in the Disk of TW Hya
摘要：
本文报道了利用阿塔卡玛大型毫米/亚毫米波天线阵对TW~Hya盘的偏振线和连续辐射的观测结果。我们以三条发射线$^{12}$ CO（3-2），$^{13}$ CO（3-2）和CS（7-6）为目标，寻找由于Goldreich-Kylafis效应引起的线偏振，同时追踪332 GHz（900 μ，\micron{}）的连续偏振形态，获得了0.5 \arcsec{}（30 μ）的空间分辨率.我们检测到线性偏振尘埃连续发射的偏振位置角显示方位角形态，和中值偏振分数为$\sim$\，0.2%，与以前的，较低的频率观测。采用“移位和堆叠”技术，以提高数据的灵敏度，结合的$Q$和$U$组件的线性组合，以考虑其方位角的依赖性，我们检测到弱的线性偏振的$^{12}$ CO和$^{13}$ CO线发射在$\sim 10σ$和$\sim 5σ$的意义，分别。在线翼中检测到偏振，对于在0.5”和1”的盘半径之间的两种分子，达到$\sim 5\%$和$\sim 3\%$的峰值偏振分数。发现偏振的符号从发射的蓝移侧翻转到红移侧，表明复杂的非对称偏振形态。对于CS发射，没有稳健地检测到偏振;然而，在$\lesssim 3σ$显著性下发现了一个在形态上与$^{12}$ CO和$^{13}$ CO发射相当的试探性信号。我们能够重建的偏振形态，与方位平均的配置文件一致，假设这也是方位对称的，这可以与未来更高的灵敏度观测。
英文摘要：
We report observations of polarized line and continuum emission from the disk of TW~Hya using the Atacama Large Millimeter/submillimeter Array. We target three emission lines, $^{12}$CO (3-2), $^{13}$CO (3-2) and CS (7-6), to search for linear polarization due to the Goldreich-Kylafis effect, while simultaneously tracing the continuum polarization morphology at 332\,GHz (900\,\micron{}), achieving a spatial resolution of 0.5\arcsec{} (30~au). We detect linear polarization in the dust continuum emission; the polarization position angles show an azimuthal morphology, and the median polarization fraction is $\sim$\,0.2\%, comparable to previous, lower frequency observations. Adopting a `shift-and-stack' technique to boost the sensitivity of the data, combined with a linear combination of the $Q$ and $U$ components to account for their azimuthal dependence, we detect weak linear polarization of $^{12}$CO and $^{13}$CO line emission at a $\sim 10σ$ and $\sim 5σ$ significance, respectively. The polarization was detected in the line wings, reaching a peak polarization fraction of $\sim 5\%$ and $\sim 3\%$ for the two molecules between disk radii of 0.5" and 1". The sign of the polarization was found to flip from the blue-shifted side of the emission to the red-shifted side, suggesting a complex, asymmetric polarization morphology. Polarization is not robustly detected for the CS emission; however, a tentative signal, comparable in morphology to that found for the $^{12}$CO and $^{13}$CO emission, is found at a $\lesssim 3σ$ significance. We are able to reconstruct a polarization morphology, consistent with the azimuthally averaged profiles, under the assumption that this is also azimuthally symmetric, which can be compared with future higher-sensitivity observations.
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