Reinvestigation of the unified theory for Seyfert galaxies by observing water vapor masers

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(1) The 20-GHz band observing system of the Tsukuba 32-m telescope of the Geographical Survey Institute was newly constructed to make observations of water-vapor maser emission in the nuclear regions of Seyfert galaxies. The HPBW of the telescope was 100" at 22 GHz, and the main beam efficiency and the aperture efficiency were 0.52 and 0.40, respectively The receiver frontend was a HEMT amplifier cooled at 20 K and had sensitivity at the radio frequencies of 19.5 - 25.2 GHz. The intermediate frequencies were 4 - 8 GHz. A spectrometer was the Fourier transformation-type digital spectrometer with the frequency band of 1 GHz and the channel number of 16 k. The system noise temperature including the atmosphere and ohmic loss was 60-80 K at the zenith. The system is useful to study the nuclear regions of Seyfert galaxies by observing water-vapor maser emission.(2) We started monitoring observations of velocities of water masers from Seyfert galaxies. In addition, we revealed that a maser disk at the center of a type 2 Seyfert, IC 1481, was thick and massive, confirming our hypothesis in which the difference between the type 1 and 2 of Seyfert galaxies is caused by not only the viewing angle of the accretion disk but also the thickness of the disk.