Global Oscillations of Maser Disks in Active Glactic Nuclei and the Kinematics of Magamaser Sources

近年来在某些第二型活动星系核（AGN）的环核区发现了水超脉泽，这为探测核的最内层秒差距开辟了一条新途径。VLBI观测揭示了脉泽辐射的详细空间分布和速度分布。一些活动星系核中的脉泽特征被发现来自于几何上薄的盘状区域。由于这样的磁盘可以通过全球m = 1振荡扰动，这是重要的是，研究这些振荡模式的特性和它们对脉泽源运动学的影响。为此，我们数值研究了m =1本征模扰动下多变圆盘中密度场和速度场的三维分布。以下是我们的结果摘要。z-对称（偏心）模式和z-反对称（翘曲）模式都存在于磁激射器圆盘中，其中z是垂直坐标。与翘曲模态相关的扰动速度场近似垂直，而与偏心模态相关的扰动速度场近似水平.受翘曲模扰动的脉泽盘的模型位置-速度图和速度漂移与开普勒盘的模型位置-速度图和速度漂移没有区别。这一特征与观测到的NGC 4258.3脉泽特征的空间和速度分布一致。在偏心模扰动下，脉泽盘的位置-速度图和速度漂移变为非开普勒。观测到的NGC 1068的亚开普勒视线速度分布可以归因于这种模式。

Recent discovery of water megamasers in circumnuclear regions of some type 2 active galactic nuclei (AGN) has opened a new way to probe the innermost parsec of the nuclei. The VLBI observations have revealed the detailed spatial and velocity distribution of the magemaser emission. Maser features in some AGN have been found to arise from geometrically thin, disk-like regions. Since such disks can be perturbed by global m = 1 oscillations, it is important to study the characteristics of these oscillation modes and their effects on the maser source kinematics. For this purpose, we have numerically studied the three dimensional distributions of the density and the velocity field in polytropic disks perturbed by the m =1 eigenmodes. The following is the summary of our results.1. Both z-symmetric (eccentric) modes and z-antisymmetric (warping) modes are present in magemaser disks, where z is the vertical coordinate. The perturbed velocity field associated with the warping mode is approximately vertical, whereas that associated with the eccentric mode is roughly horizontal.2. The model position-velocity diagram and velocity drift for maser disks perturbed by the warping mode are indistinguishable from those of Keplerian disks. This characteristic agrees well with the observed spatial and velocity distribution of the maser features of NGC 4258.3. In maser disks perturbed by the eccentric mode, the position-velocity diagram and the velocity drift become non-Keplerian. The observed sub-Keplerian line-of-sight velocity distribution of NGC 1068 can be attributed to this mode.