A synergy of the velocity gradients technique and the probability density functions for identifying gravitational collapse in self-absorbing media
A synergy of the velocity gradients technique and the probability density functions for identifying gravitational collapse in self-absorbing media
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DOI：
10.1093/mnras/stab087
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发表时间：
2021-02
影响因子：
4.8
通讯作者：
Yue Hu;A. Lazarian
中科院分区：
文献类型：
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作者：
Yue Hu;A. Lazarian
速度矢量技术（VGT）和质量密度的概率密度函数（PDF）是研究分子云中湍流、磁场和自引力的工具。然而，自吸收可以显着地使观察到的强度不同于柱密度结构。在这项工作中，我们研究了自吸收对VGT和强度PDF的影响，利用三个合成的CO同位素$^{12}$CO（1-0），$^{13}$CO（1-0），和C$^{18}$O（1-0）的发射线。我们确认VGT的性能是不敏感的辐射传递效应。我们数值计算表明，通过VGT构建三维磁场层析成像的可能性。我们发现，强度PDF改变其形状从纯对数正态分布，表现出幂律尾取决于光学深度的超音速湍流。结果表明，CO同位素密度函数的变化与自引力无关，这使得密度函数在识别引力坍缩区时的可靠性降低。我们计算了恒星形成区NGC 1333的强度PDF，发现强度PDF在观测中的变化与我们的数值结果一致。VGT和柱密度PDF的协同作用证实了自引力气体在NGC 1333中占据了很大的体积。
The Velocity Gradients Technique (VGT) and the Probability Density Functions (PDFs) of mass density are tools to study turbulence, magnetic fields, and self-gravity in molecular clouds. However, self-absorption can significantly make the observed intensity different from the column density structures. In this work, we study the effects of self-absorption on the VGT and the intensity PDFs utilizing three synthetic emission lines of CO isotopologs $^{12}$CO (1-0), $^{13}$CO (1-0), and C$^{18}$O (1-0). We confirm that the performance of VGT is insensitive to the radiative transfer effect. We numerically show the possibility of constructing 3D magnetic fields tomography through VGT. We find that the intensity PDFs change their shape from the pure log-normal to a distribution that exhibits a power-law tail depending on the optical depth for supersonic turbulence. We conclude the change of CO isotopologs' intensity PDFs can be independent of self-gravity, which makes the intensity PDFs less reliable in identifying gravitational collapsing regions. We compute the intensity PDFs for a star-forming region NGC 1333 and find the change of intensity PDFs in observation agrees with our numerical results. The synergy of VGT and the column density PDFs confirms that the self-gravitating gas occupies a large volume in NGC 1333.