七个活动星系核中极端H$\alpha$线轮廓的光学光谱偏振测量
Optical spectropolarimetry of extreme H$α$ line profiles in seven active galactic nuclei
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中文总结 AI 辅助
针对七个亮塞弗特1星系极端不对称H$\alpha$线，通过VLT/FORS2光谱偏振测量和谱分解，揭示宽线区两种散射几何行为，支持盘风模型。
中文摘要 AI 辅助
一些活动星系核（AGNs）已知会表现出极不对称的宽巴耳末线，其主峰红移或蓝移达数千公里每秒（km s$^{-1}$），这严重挑战了我们对标准活动星系核范式的理解。我们希望通过对一个具有已知极端巴耳末线轮廓的亮活动星系核样本进行光谱偏振研究，来探索这种不对称特征的成因。我们展示了2012年3月至2013年1月期间使用甚大望远镜（VLT）上的低色散光谱仪2（FORS2）获得的七个明亮（V $<$ 17.5）塞弗特1星系的光学光谱偏振数据。主要宽巴耳末线（H$\alpha$和H$\beta$，偶尔包括H$\gamma$）以350至500的分辨率进行了采样。我们对每个H$\alpha$轮廓进行了详细的谱分解，以分离宽线区（BLR）内的运动学子结构，并测量了每个分量的偏振度和偏振角，从而对内部几何结构和散射特性提供了约束。宽H$\alpha$分量表现出多种散射几何。其偏振作为半高全宽（FWHM）的函数揭示了两种不同的行为，分别对应于具有大致恒定标高（scale height）的宽线区，或具有在更高速度下高度减小的分层结构。这支持了连接赤道区和极区的盘风（disk-wind）几何模型。
英文摘要
Some active galactic nuclei (AGNs) are known to show extremely asymmetric broad Balmer lines, with their main peak redshifted or blueshifted by thousands of km s$^{-1}$, severely challenging our understanding of the standard AGN paradigm. We wanted to explore the causes of such asymmetric features by carrying out a spectropolarimetric study of a sample of bright AGNs with known extreme Balmer line profiles. We present optical spectropolarimetry of seven bright (V $<$ 17.5) Seyfert-1 galaxies obtained with the Very Large Telescope (VLT) FOcal Reducer/low dispersion Spectrograph 2 (FORS2) instrument from March 2012 to January 2013. The main broad Balmer lines (H$α$ and H$β$, and H$γ$ occasionally) were sampled with a resolving power ranging from 350 to 500. We performed a detailed spectral decomposition of each H$α$ profile to isolate kinematic substructures within the broad line region (BLR) and measured the polarization degree and angle of each component, providing constraints on the inner geometry and scattering properties. The broad H$α$ components exhibit various scattering geometries. Their polarization as a function of full width at half maximum (FWHM) reveals two distinct behaviors, corresponding to either a BLR of roughly constant scale height or a stratified structure with decreasing height at higher velocities. This supports a disk-wind geometry linking equatorial and polar regions.
发表机构
- Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg（斯特拉斯堡大学）
- Institut d’Astrophysique et de Géophysique, Université de Liège（列日大学天体物理学与地球物理学研究所）
- Department of Astronomy and Astrophysics, University of California at Santa Cruz（加州大学圣克鲁斯分校天文学与天体物理系）
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