Observational and theoretical studies of high-velocity components of extragalactic water masers

1992年，NGC4258中的水脉波被发现表现出极高的速度特征，约为1000km/s，这比普通水脉波的流出速度大得多。为了解释这一现象，我们从观测和理论两方面研究了星系核周围旋转盘的脉泽模型，或拉曼散射引起的频移模型。首先，我们研究了等离子体中的拉曼散射模型，并找到了等离子体密度和温度所需的条件（Deguchi 1994）。本文预测，如果这个模型是正确的，NGC4258中极高速成分的发射会有轻微的极化。我们在美国Haystack用37m射电望远镜进行了偏振观测，两次观测结果表明，线偏振度小于20% （Deguchi 1995）。结果表明，在强磁场中，由于法拉第退极化，线极化消失。Miyoshi et al.（1995）利用美国甚长基线阵列对极速分量进行了位置测量，发现极速分量来自与主分量相距3毫弧秒的位置。虽然Watson和Walin提出了一个可以提供斑点位置和速度之间条件的旋转盘模型，但我们已经证明，简单的盘模型必须加入盘旋转的翘曲运动，它不能解释蓝移特征的弱点。此外，为了研究天体物理微波激射器的一般性质，我们与Dr.A.M.Sobolev一起研究了微波激射器（特别是甲醇微波激射器）的抽运机制。我们还与印度天体物理研究所的r.t. gangadhara博士一起研究了拉曼散射脉泽。

In 1992, water masers in NGC4258 was discoverd to exhibit extreme high velocity features of about 1000km/s, which is much larger than the outflow velocity of normal water masers. For the explanation of this phenomena, we have studied the models of masers from a rotating disk around the galactic nucleus, or models of the frequncy shift due to Raman scattering, both observationally and theoretically. First, we have investigated the model of Raman scattering in plasma and found what conditions are required for the density and temperature of the plasma (Deguchi 1994). It was predicted in this paper that, if this model is correct, emission from extreme high velocity components in NGC4258 is slightly polarized. We have performed the polarization observationswith the 37m radio telescope at Haystack, U.S.A.It has turned out in two sessions of observations that the degree of linear polarization is less than 20% (Deguchi 1995). This reult indicates that the linear polarization disappears due to the Farady depolarization in the strong magnetic field. Miyoshi et al. (1995) have performed position measurements of extreme velocity components with U.S.Very Long Baseline Array and found that the extreme components come from the position by 3 milli-arcsec separated from the main components. Though Watson and Walin proposed a rotating disk model which can provide the condition between positions and velocities of spots, we have shown that the simple disk model have to add the warp motion of the disk rotation and it cannot explain the weakness of the blue -shifted feature. In addition, to investigate the general properties of astrophysiccal masers, we have investigated the pumping mechanism of masers (especially for the methanol masers) with Dr.A.M.Sobolev. We have also worked on the Raman scattering masers with Dr.R.T.Gangadhara in Indian Institute of Astrophysics.