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

最近在一些类型的2型活动星系核(AGN)的核周区域发现了水巨型激光器，这为探测这些核的最内侧部分开辟了一条新的途径。VLBI观测揭示了磁脉泽发射的详细空间和速度分布。一些活动星系核中的脉泽特征被发现来自几何上很薄的盘状区域。由于这类圆盘可能受到全球m=1振荡的扰动，因此研究这些振荡模式的特征及其对脉泽源运动学的影响是很重要的。为此，我们数值研究了受m=1个本征模扰动的多变圆盘中密度场和速度场的三维分布。以下是我们研究结果的总结。Z对称(偏心)模和z反对称(翘曲)模都存在于磁脉泽盘中，其中z是垂直坐标。与翘曲模式相关的扰动速度场近似为垂直，而与偏心模式相关的扰动速度场则大致为水平。受翘曲模式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位置-速度图和速度漂移难以区分。这一特征与观测到的NGC 4258.3脉泽特征的空间和速度分布很好地吻合。在受偏心模式扰动的脉泽盘中，位置-速度图和速度漂移变为非开普勒量。观测到的NGC1068的亚开普勒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.