Magnetic Fields in the Early Stages of Massive Star Formation as Revealed by ALMA
Magnetic Fields in the Early Stages of Massive Star Formation as Revealed by ALMA
复制标题
DOI：
10.3847/1538-4357/ab9087
复制
发表时间：
2020-05
期刊：
影响因子：
--
通讯作者：
Junhao Liu;Qizhou Zhang;K. Qiu;Hauyu Baobab Liu;T. Pillai;Josep Miquel Girart;Zhi-Yun Li;Ke Wang
中科院分区：
文献类型：
--
作者：
Junhao Liu;Qizhou Zhang;K. Qiu;Hauyu Baobab Liu;T. Pillai;Josep Miquel Girart;Zhi-Yun Li;Ke Wang
我们在红外黑云G28.34+0.06中以~ 0.02 pc的分辨率对三个大质量分子团MM1、MM4和MM9进行了1.3 mm ALMA尘埃偏振观测。利用这些敏感的高分辨率连续体数据，MM1被分解成凝聚团。每个团块中的磁场结构通过极化发射揭示出来。在MM1和MM4中，随着Stokes I强度的增加，极化发射分数呈下降趋势。利用角色散函数法（一种改进的Davis-Chandrasekhar-Fermi方法），估计两个大质量致密核MM1-Core1和MM4-Core4的天平面磁场强度分别为~ 1.6 mG和~ 0.32 mG。MM1-Core1和MM4-Core4的viral参数分别为~ 0.76和~ 0.37，表明大质量恒星的形成不是在平衡状态下开始的。利用极化-强度梯度-局部重力方法，我们发现在三个团块中，局部重力与强度梯度密切相关，并且在MM1和MM4中，磁场除靠近发射峰的区域外，都倾向于与局部重力对齐，说明重力在气体坍缩的调节中起主导作用。发现MM4和MM9中有一半的流出物排列在冷凝尺度磁场的10°范围内（<0.05 pc），这表明在大质量恒星形成的早期，从冷凝到盘尺度，磁场可能发挥了重要作用。
We present 1.3 mm ALMA dust polarization observations at a resolution of ∼0.02 pc for three massive molecular clumps, MM1, MM4, and MM9, in the infrared dark cloud G28.34+0.06. With these sensitive and high-resolution continuum data, MM1 is resolved into a cluster of condensations. The magnetic field structure in each clump is revealed by the polarized emission. We found a trend of decreasing polarized emission fraction with increasing Stokes I intensities in MM1 and MM4. Using the angular dispersion function method (a modified Davis–Chandrasekhar–Fermi method), the plane-of-sky magnetic field strengths in two massive dense cores, MM1-Core1 and MM4-Core4, are estimated to be ∼1.6 mG and ∼0.32 mG, respectively. The virial parameters in MM1-Core1 and MM4-Core4 are calculated to be ∼0.76 and ∼0.37, respectively, suggesting that massive star formation does not start in equilibrium. Using the polarization-intensity gradient-local gravity method, we found that the local gravity is closely aligned with intensity gradient in the three clumps, and the magnetic field tends to be aligned with the local gravity in MM1 and MM4 except for regions near the emission peak, which suggests that the gravity plays a dominant role in regulating the gas collapse. Half of the outflows in MM4 and MM9 are found to be aligned within 10° of the condensation-scale (<0.05 pc) magnetic field, indicating that the magnetic field could play an important role from condensation to disk scale in the early stage of massive star formation.