The origin of dust polarization in molecular outflows
The origin of dust polarization in molecular outflows
复制标题
分子流出中尘埃极化的起源
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
R. Klessen
中科院分区：
文献类型：
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作者：
S. Reissl;S. Reissl;D. Seifried;S. Wolf;R. Banerjee;R. Klessen
目的：在本文中，我们提出了一个案例研究，调查必要的条件，以检测嵌入在一个大规模的领域的特征磁场子结构。螺旋磁场与周围的沙漏形场预计从理论预测和自洽磁流体动力学（MHD）模拟是目前在特定情况下的原恒星外流。因此，这样的外流环境是我们研究的最佳环境。方法：我们提出了合成偏振图在红外和毫米制度的原恒星流出与新开发的RT和偏振代码POLARIS。该代码，作为第一个，包括一个自洽的描述，如不完美的戴维斯-格林斯坦（IDG）和辐射扭矩（RAT）对齐的各种执行机制。我们研究了影响晶粒尺寸分布的因素，以及应用的消除机制。结果如下：我们发现IDG机制无法产生任何可测量的极化度（<1%），而RAT对齐产生的极化度只有几个1%。此外，我们开发了一种方法来识别偏振的起源。我们发现，在流出的螺旋磁场只能观察到接近流出轴，并在其尖端，而在周围地区的沙漏领域的前景占主导地位的极化。此外，出流瓣中的偏振度比周围的偏振度低，与观测结果一致。我们还发现，由于从二向色性消光到热再发射的过渡，偏振矢量的方向翻转了大约100微米。因此，为了避免解释偏振数据时的模糊性，我们建议在远红外和毫米波段进行观察。最后，我们表明，与阿尔马，它是可以观察到的极化出现从原恒星流出。
Aims: In this paper we present a case study to investigate conditions necessary to detect a characteristic magnetic field substructure embedded in a large-scale field. A helical magnetic field with a surrounding hourglass shaped field is expected from theoretical predictions and self-consistent magnetohydrodynamical (MHD) simulations to be present in the specific case of protostellar outflows. Hence, such an outflow environment is the perfect for our study. Methodes: We present synthetic polarisation maps in the infrared and millimeter regime of protostellar outflows performed with the newly developed RT and polarisation code POLARIS. The code, as the first, includes a self-consistent description of various alignement mechanism like the imperfect Davis-Greenstein (IDG) and the radiative torque (RAT) alignment. We investigate for which effects the grain size distribution, and applied alignement mechanism have. Results: We find that the IDG mechanism cannot produce any measurable polarization degree (< 1 %) whereas RAT alignment produced polarization degrees of a few 1 %. Furthermore, we developed a method to identify the origin of the polarization. We show that the helical magnetic field in the outflow can only be observed close to the outflow axis and at its tip, whereas in the surrounding regions the hourglass field in the foreground dominates the polarization. Furthermore, the polarization degree in the outflow lobe is lower than in the surroundings in agreement with observations. We also find that the orientation of the polarization vector flips around a few 100 micron due to the transition from dichroic extinction to thermal re-emission. Hence, in order to avoid ambiguities when interpreting polarization data, we suggest to observed in the far-infrared and mm regime. Finally, we show that with ALMA it is possible to observe the polarization emerging from protostellar outflows.