漫射星际介质中辐射力矩晶粒排列的系统研究
A systematic study of radiative torque grain alignment in the diffuse interstellar medium
摘要：
上下文普朗克观测表明，在漫反射ISM中，晶粒的排列效率几乎是恒定的。目的。我们测试，如果辐射扭矩（RAT）的理论是兼容的观测约束晶粒排列。方法.我们结合了数值模拟与辐射转移代码POLARIS，其中包括一个物理尘埃模型和详细的晶粒排列物理的RAT。尘埃模型的目的是再现光谱依赖的消光的ISM。从星际湍流的RAMSES模拟，我们提取一个立方体的漫ISM代表。我们用POLARIS对立方体进行后处理，得到颗粒温度和RAT，以模拟合成尘埃偏振图。结果在我们的模拟中，晶粒排列效率与气体压力相关，但与RAT强度无关。由于尘埃消光较低，RAT的大小变化不大，仅在高气柱密度$N_H$时减小。比较我们的地图与统一的对齐效率，我们没有发现系统的差异。偏振分数$p$与$N_H$或偏振色散$S$的依赖性是相似的。密集区域中RAT的下降几乎不影响极化图案，信号由LOS和磁场几何形状支配。如果插入一颗恒星，偏振会增加，恒星周围没有特定的图案。在标测图中未观察到RAT的角度依赖性，并且使用均匀磁场时该角度依赖性较弱。结论. RAT是兼容的普朗克数据的扩散ISM，这样的均匀对齐和RAT对齐导致类似的意见。为了进一步测试RAT的预测，其中一个重要的下降的晶粒排列是预期的，密集地区的偏振观测必须面对的数值模拟采样高柱密度通过密集的云，有足够的统计数据。
英文摘要：
Context. Planck observations demonstrated that the grain alignment efficiency is almost constant in the diffuse ISM. Aims. We test if the Radiative Torque (RAT) theory is compatible with observational constraints on grain alignment. Methods. We combine a numerical simulation with the radiative transfer code POLARIS that incorporates a physical dust model and the detailed grain alignment physics of RATs. A dust model is designed to reproduce the spectral dependence of extinction of the ISM. From a RAMSES simulation of interstellar turbulence, we extract a cube representative of the diffuse ISM. We post-process the cube with POLARIS to get the grain temperature and RATs to simulate synthetic dust polarization maps. Results. In our simulation the grain alignment efficiency is correlated with gas pressure, but not with the RAT intensity. Because of the low dust extinction, the magnitude of RATs varies little, decreasing only for high column densities $N_H$. Comparing our maps with a uniform alignment efficiency, we find no systematic difference. The dependence of polarization fraction $p$ with $N_H$ or polarization dispersion $S$ is similar. The drop of RATs in dense regions barely affects the polarization pattern, the signal being dominated by the LOS and magnetic field geometry. If a star is inserted, the polarization increases, with no specific pattern around the star. The angle-dependence of RATs is not observed in the maps, and is weak using a uniform magnetic field. Conclusions. RATs are compatible with Planck data for the diffuse ISM such that both uniform alignment and RAT alignment lead to similar observations. To further test the predictions of RATs where an important drop of grain alignment is expected, polarization observations of dense regions must be confronted to numerical simulations sampling high column densities through dense clouds, with enough statistics.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
