Polarization of Absorption Lines as a Diagnostics of Circumstellar, Interstellar, and Intergalactic Magnetic Fields: Fine-Structure Atoms
Polarization of Absorption Lines as a Diagnostics of Circumstellar, Interstellar, and Intergalactic Magnetic Fields: Fine-Structure Atoms
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吸收线的极化作为星周、星际和星系间磁场的诊断：精细结构原子
DOI：
10.1086/508704
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
A. Lazarian
中科院分区：
文献类型：
--
作者：
Huirong Yan;A. Lazarian
原子基态精细结构亚能级的相对居数受到各向异性辐射通量引起的辐射跃迁的影响。这导致了原子角动量的排列。就星际和星系间介质的观测结果而言，这导致了吸收线的极化。在本文中，我们考虑了产生这种效应的必要条件，并提供了几个具有多个上下能级的天体物理上重要的原子和离子对任意方向的磁场的偏振计算(1)光泵浦源，(2)观测方向，(3)吸收源。我们还考虑了一个天体物理学上重要的“简并”情况，其中光泵浦源与吸收辐射源重合。我们提出了线性极化程度和吸收强度与磁场的三维方向有关的解析表达式，这些方向与泵浦源、吸收辐射源和观测方向有关。我们讨论了如何通过同时观察几条吸收线来确定所有这些参数，并提出了有助于实际数据解释的图形方法。我们证明了吸收线极化的研究为研究各种天体物理条件下的三维磁场拓扑结构提供了一个独特的工具。
The relative population of the fine-structure sublevels of an atom's ground state is affected by radiative transitions induced by an anisotropic radiation flux. This causes the alignment of atomic angular momentum. In terms of observational consequences for the interstellar and intergalactic medium, this results in the polarization of the absorption lines. In the paper we consider the conditions necessary for this effect and provide calculations of polarization from a few astrophysically important atoms and ions with multiple upper and lower levels for an arbitrary orientation of magnetic fields to the (1) source of optical pumping, (2) direction of observation, and (3) absorbed source. We also consider an astrophysically important "degenerate" case, in which the source of optical pumping coincides with the source of the absorbed radiation. We present analytical expressions that relate the degree of linear polarization and the intensity of absorption to the three-dimensional orientation of the magnetic field with respect to the pumping source, the source of the absorbed radiation, and the direction of observations. We discuss how all these parameters can be determined via simultaneous observations of several absorption lines and suggest graphical means that are helpful in practical data interpretation. We prove that studies of absorption line polarization provide a unique tool to study three-dimensional magnetic field topology in various astrophysical conditions.