Interferometric Observations of Magnetic Fields in Forming Stars
Interferometric Observations of Magnetic Fields in Forming Stars
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DOI：
10.3389/fspas.2019.00003
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发表时间：
2019-03
影响因子：
3
通讯作者：
C. Hull;Qizhou Zhang
中科院分区：
文献类型：
--
作者：
C. Hull;Qizhou Zhang
磁场是星星形成的关键因素。在过去的二十年里，毫米波和亚毫米波干涉仪在揭示磁场在星星形成中的作用方面取得了重大进展，空间尺度越来越小。从千秒差距尺度的分子云到内部的几百个Au，在毫米和亚毫米波长下的偏振主要是由偏振的热尘埃辐射决定的，尘埃颗粒相对于磁场排列。干涉测量研究的重点是这种尘埃偏振，偶尔对偏振的光谱线发射。我们回顾了磁化星星形成领域的几个问题的背景下，继续激励研究的高质量和低质量的星星的形成。通过对单个研究结果的汇总和分析，我们得出以下结论：（1）低质量原恒星核的磁场和外流是随机排列的，表明~1000 Au尺度的磁场不是决定嵌入盘和外流角动量的主导因素。(2)最近对大质量恒星形成区的热力学和动力学性质的测量揭示了小维里参数，挑战了平衡态星星形成的假设。然而，我们估计，这些物体中几分之一mG到几mG的磁场强度可以使致密气体接近平衡状态。最后，（3）我们发现，在0.01 - 0.1 pc尺度下，具有沙漏形磁场形态的少数源不能纯粹用投影效应来解释，这表明虽然偶尔会发生，但磁主导的核心坍缩并不是低质量或高质量星星形成的主要模式。[摘要]
The magnetic field is a key ingredient in the recipe of star formation. Over the past two decades, millimeter and submillimeter interferometers have made major strides in unveiling the role of the magnetic field in star formation at progressively smaller spatial scales. From the kiloparsec scale of molecular clouds down to the inner few hundred au immediately surrounding forming stars, the polarization at millimeter and submillimeter wavelengths is dominated by polarized thermal dust emission, where the dust grains are aligned relative to the magnetic field. Interferometric studies have focused on this dust polarization and occasionally on the polarization of spectral-line emission. We review the current state of the field of magnetized star formation in the context of several questions that continue to motivate the studies of high- and low-mass star formation. By aggregating and analyzing the results from individual studies, we come to several conclusions: (1) Magnetic fields and outflows from low-mass protostellar cores are randomly aligned, suggesting that the magnetic field at ~1000 au scales is not the dominant factor in setting the angular momentum of embedded disks and outflows. (2) Recent measurements of the thermal and dynamic properties in high-mass star-forming regions reveal small virial parameters, challenging the assumption of equilibrium star formation. However, we estimate that a magnetic field strength of a fraction of a mG to several mG in these objects could bring the dense gas close to a state of equilibrium. Finally, (3) We find that the small number of sources with hourglass-shaped magnetic field morphologies at 0.01 -- 0.1 pc scales cannot be explained purely by projection effects, suggesting that while it does occur occasionally, magnetically dominated core collapse is not the predominant mode of low- or high-mass star formation. [Abridged]