POLARIZATION OF LYMAN α EMERGENT FROM A THICK SLAB OF NEUTRAL HYDROGEN

IF 1.1 4区 物理与天体物理 Q3 ASTRONOMY & ASTROPHYSICS
S. Ahn, Hee-Won Lee
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引用次数: 7

Abstract

Star forming galaxies found in the early universe exhibit asymmetric Lyα emission line that results from multiple scattering in a neutral thick medium surrounding the Lyα emission source. It is expected that emergent Lyα will be significantly polarized through a large number of resonance scattering events followed by a number of successive wing scatterings. In this study we adopt a Monte Carlo method to calculate the polarization of Lyα transferred in a very thick static slab of Hi. Resonantly scattered radiation associated with transitions between 1S½? 2P½ ,3/2 is only weakly polarized and therefore linear polarization of the emergent Lyα is mainly dependent on the number of off-resonant wing scattering events. The number of wing scattering events just before escape from the slab is determined by the product of the Doppler parameter a and the line center optical depth τ0, which, in turn, determines the behavior of the linear polarization of Lyα. This result is analogous to the study of polarized radiative transfer of Thomson scattered photons in an electron slab, where the emergent photons are polarized in the direction perpendicular to the slab when the scattering optical depth is small and polarized in the parallel direction when the slab is optically thick. Our simulated spectropolarimetry of Lyα shows that the line center is negligibly polarized, the near wing parts polarized in the direction parallel to the slab and the far wing parts are polarized in the direction perpendicular to the slab. We emphasize that the flip of polarization direction in the wing parts of Lyα naturally reflects the diffusive nature of the Lyα transfer process in thick neutral media.
中性氢厚板产生的莱曼α的极化
在早期宇宙中发现的恒星形成星系表现出不对称的Lyα发射线,这是由Lyα发射源周围中性厚介质的多次散射造成的。预计通过大量的共振散射事件和一系列连续的机翼散射,涌现的Lyα将被显著极化。本文采用蒙特卡罗方法计算了Lyα在极厚的Hi静态板中传递的极化。共振散射辐射与1S / 2 ?2P 1 /2,3/2只有弱极化,因此Lyα的线性极化主要取决于非共振翼散射事件的数量。逃逸前的翼散射事件数由多普勒参数a与线中心光深τ0的乘积决定,而线中心光深τ0又决定Lyα的线偏振特性。这一结果类似于研究汤姆逊散射光子在电子板中的偏振辐射转移,当散射光学深度小时,出射光子在垂直于平板的方向上偏振,当平板光学厚度大时,出射光子在平行方向上偏振。我们对Lyα的模拟偏振分析表明,线中心的偏振可以忽略不计,近翼部分在平行于平板的方向上偏振,远翼部分在垂直于平板的方向上偏振。我们强调,Lyα翼部极化方向的翻转自然地反映了Lyα在厚中性介质中传递过程的扩散性质。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of the Korean Astronomical Society
Journal of the Korean Astronomical Society 地学天文-天文与天体物理
CiteScore
1.30
自引率
10.00%
发文量
0
审稿时长
>12 weeks
期刊介绍: JKAS is an international scientific journal publishing papers in all fields of astronomy and astrophysics. All manuscripts are subject to the scrutiny of referees. Manuscripts submitted to JKAS must comply with the ethics policy of JKAS. Six regular issues are published each year on February 28, April 30, June 30, August 31, October 31, and December 31. One year''s issues compose one volume.
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