Megamaser Cosmology Project。VII。利用光谱监测观测研究磁盘物理学
The Megamaser Cosmology Project. VII. Investigating disk physics using spectral monitoring observations
摘要：
我们使用单碟射电光谱已知的22 GHz H $_2$ O超脉泽，主要是从大型数据集收集观测的超脉泽宇宙学项目，以确定开普勒吸积盘，并调查几个方面的磁盘物理。我们测试了Maoz和McKee（1998）提出的脉泽激发机制，即粒子数反转发生在穿过圆盘的螺旋激波后面的气体中。虽然红移特征的通量平均比蓝移特征的通量大，但在模型的支持下，高速特征没有显示出预测的系统速度漂移。我们发现ESO 558-G 009脉泽光谱的快速日内变化很可能是星际闪烁的结果，为此我们倾向于附近的（$D \approx 70$ pc）散射屏。在搜索混响在六个良好的采样源，我们发现，任何径向传播的信号必须贡献$\lesssim$ 10%的总变异性。我们还设置了七个源的磁场强度的限制，使用强耀斑事件来检查塞曼分裂的存在。这些极限通常是200- 300 mG（$1σ$），但我们对星系NGC 1194的最严格极限可达73 mG。
英文摘要：
We use single-dish radio spectra of known 22 GHz H$_2$O megamasers, primarily gathered from the large dataset observed by the Megamaser Cosmology Project, to identify Keplerian accretion disks and to investigate several aspects of the disk physics. We test a mechanism for maser excitation proposed by Maoz & McKee (1998), whereby population inversion arises in gas behind spiral shocks traveling through the disk. Though the flux of redshifted features is larger on average than that of blueshifted features, in support of the model, the high-velocity features show none of the predicted systematic velocity drifts. We find rapid intra-day variability in the maser spectrum of ESO 558-G009 that is likely the result of interstellar scintillation, for which we favor a nearby ($D \approx 70$ pc) scattering screen. In a search for reverberation in six well-sampled sources, we find that any radially-propagating signal must be contributing $\lesssim$10% of the total variability. We also set limits on the magnetic field strengths in seven sources, using strong flaring events to check for the presence of Zeeman splitting. These limits are typically 200--300 mG ($1σ$), but our most stringent limits reach down to 73 mG for the galaxy NGC 1194.
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