PolCat: Modelling submillimetre polarization of molecular cloud cores using successive parametrized coordinate transformations
PolCat: Modelling submillimetre polarization of molecular cloud cores using successive parametrized coordinate transformations
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DOI：
10.1093/mnras/stw3380
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发表时间：
2016-12
影响因子：
4.8
通讯作者：
E. Franzmann;J. Fiege
中科院分区：
文献类型：
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作者：
E. Franzmann;J. Fiege
我们介绍了一个名为polcat的软件包，用于使用亚毫米线性极化和热尘埃发射的连续强度图来模拟磁化的分子云核心。我们的polcatmodeling软件通过使用连续参数化坐标变换建立三维三轴核心模型，并生成模拟偏振图以适应观测数据集。我们利用多目标进化优化器搜索参数空间，以同时最小化强度和极化位置角图的χ2。本文的目的是通过将其应用于几个人工数据集来进行测试，使用大约400个测试运行来描述代码的功能和性能。我们发现，极化能够区分扭曲和非扭曲场几何的极化映射，并在数据中存在扭曲时识别出扭曲的对称性。当与具有正确场几何形状的模型相拟合时，polcat通常可以得到正确的岩心形状。我们描述了我们的模型由于取向的简并性，发现至少有八个简并的岩心取向产生相同的极化图对于三轴岩心的情况。简并度随核对称而增大。我们期望偏振能成为一个有用的工具来模拟观测偏振数据集。我们的测试表明，代码通常可以消除不正确的字段配置，同时找到可以解释数据的范围或潜在模型。物理方面的考虑通常可以进一步减少允许的模型集，从而对现场几何形状产生合理的约束。
We introduce a software package calledpolcatfor modelling magnetized molecular cloud cores using submillimetre linear polarization and continuum intensity maps from thermal dust emission. Ourpolcatmodelling software builds a three-dimensional triaxial core model via the use of consecutive parametrized coordinate transformations, and produces simulated polarization maps to fit to observational data sets. We utilize a multi-objective evolutionary optimizer to search the parameter space to simultaneously minimize χ2for the intensity and polarization position angle maps. The aim of this paper is to testpolcatby applying it to several artificial data sets, characterizing the capabilities and performance of the code using approximately 400 test runs. We find thatpolcatis able to distinguish between polarization maps of twisted and non-twisted field geometries and identify the symmetry of the twist when one exists in the data.polcatgenerally obtains the correct shapes of cores when fitted to models with the correct field geometry. We characterized the degeneracy of our models due to orientation, finding that there are at least eight degenerate core orientations that produce identical polarization maps for the case of triaxial cores. The degeneracy increases with core symmetry. We expectpolcatto be a useful tool for modelling observational polarization data sets. Our tests demonstrate that the code can often eliminate incorrect field configurations, while finding a range or potential models that can explain the data. Physical considerations can often further reduce the set of allowed models, resulting in reasonable constraints on field geometry.