双峰巴耳末发射线活动星系核的长期廓线变率
Long-Term Profile Variability in Active Galactic Nuclei with Double-Peaked Balmer Emission Lines
摘要：
越来越多的活动星系核（AGN）表现出宽的双峰巴耳末发射线，这是活动星系核中存在相对大尺度吸积盘的最好证据。一组20个双峰发射器已被监测了近十年，以观察双峰巴耳末线的轮廓的长期变化。变化一般以年为单位，归因于吸积盘的物理变化。在这里，我们描述了一个子集的七个双峰发射器在一个模型独立的方式的变异性。我们发现，变异性主要是由一个或多个离散的过量排放“块”的存在引起的;在一年（有时更短）的时间尺度上，这些块的振幅和形状发生变化，但这些块的预计速度在更长的时间尺度上（几年）发生变化。我们还发现，所有的对象都表现出红色的峰值比蓝色的峰值在某些时期和/或蓝移的整体配置文件，相反的期望一个简单的，圆形的吸积盘模型，从而强调需要在吸积盘的不对称性。与两个简单的模型，一个椭圆形的吸积盘和一个圆盘与螺旋臂的比较，是无法重现所观察到的变化的所有方面，虽然都占了一些观察到的行为。七个物体中有三个对黑洞质量有可靠的估计。对于这些对象所观察到的变化时间尺度是一致的预期旋臂的岁差时间尺度，但不兼容的椭圆形吸积盘。我们认为，通过简单的修改，允许螺旋臂被分割，许多观察到的变异模式可以复制。
英文摘要：
An increasing number of Active Galactic Nuclei (AGNs) exhibit broad, double-peaked Balmer emission lines,which represent some of the best evidence for the existence of relatively large-scale accretion disks in AGNs. A set of 20 double-peaked emitters have been monitored for nearly a decade in order to observe long-term variations in the profiles of the double-peaked Balmer lines. Variations generally occur on timescales of years, and are attributed to physical changes in the accretion disk. Here we characterize the variability of a subset of seven double-peaked emitters in a model independent way. We find that variability is caused primarily by the presence of one or more discrete "lumps" of excess emission; over a timescale of a year (and sometimes less) these lumps change in amplitude and shape, but the projected velocity of these lumps changes over much longer timescales (several years). We also find that all of the objects exhibit red peaks that are stronger than the blue peak at some epochs and/or blueshifts in the overall profile, contrary to the expectations for a simple, circular accretion disk model, thus emphasizing the need for asymmetries in the accretion disk. Comparisons with two simple models, an elliptical accretion disk and a circular disk with a spiral arm, are unable to reproduce all aspects of the observed variability, although both account for some of the observed behaviors. Three of the seven objects have robust estimates of the black hole masses. For these objects the observed variability timescale is consistent with the expected precession timescale for a spiral arm, but incompatible with that of an elliptical accretion disk. We suggest that with the simple modification of allowing the spiral arm to be fragmented, many of the observed variability patterns could be reproduced.
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