@misc{oai:ir.soken.ac.jp:00000379,
 author = {萩原, 喜昭 and ハギワラ, ヨシアキ and HAGIWARA, Yoshiaki},
 month = {2016-02-17, 2016-02-17},
 note = {Many attempts have been made so far to study properties and kinematical distributions of interstellar matter in the circumnuclear region of radio-quiet galaxies using interferometers with high angular resolution. However, compared to a variety of samples of radio-quiet galaxies, samples of radio-active galaxies have few detections, compared to radio-quiet galaxies, because of the low gas mass and larger distances to the galaxies. To detect molecular gas in radio-active galaxies, we need a new interferometer with higher sensitivity than existing arrays. 
   I devoted myself to the construction of the extended millimeter array system, Rainbow Array system, on the basis of existing Nobeyama Millimeter Array(NMA). The Rainbow Array consists of the six 10 m radio telescopes and the 45 m telescope in Nobeyama Radio Observatory. I contributed to the instrumentation development, including building the SIS receiver and its electronics, the design of the optics, and installing these instruments. After constructing the array system, the system tests were conducted to verify the whole array system. The use of the 45 m telescope with NMA resulted in a great improvement in the sensitivity. Finally, I have employed the Rainbow Array to observe the radio galaxy NGC 1275 in the CO (J = 1 → 0) transition. 
   The observations of NGC 1275 were carried out at an angular resolution of ～ one arcsecond with the Rainbow Array, using self-calibration to minimize baseline calibration errors which mainly arise from uncertainties of 45 m - 10 m baselines. 
   The CO line emission of NGC 1275 was found to be concentrated in the central r < 400 pc region around the nucleus. The total molecular mass estimated from the line intensity is ～ 10<SUP>9</SUP> M〓. This value is only 4.5% of the molecular mass estimated from the previous observations within the central 10 kpc region. Although there are some discrepancies between my results with those in published images, the follow-up NMA observations confirmed that the image obtained with the Rainbow is reliable. 
   The CO twin peaks structure with a radius of 1.2 kpc from the nucleus reported by Inoue et al. (1996) and the newly detected CO central concentration seem to imply that the detected central CO emission could be the result of gas fueling from the outer molecular gas ring structure, by analogy with the Seyfert galaxy NGC 1068. The central unresolved CO emission peak could form the molecular torus which obscures the central engine from our direct view. It is very interesting that the circumnuclear gas surrounding the radio-loud nucleus has a very similar morphology to that around the radio-quiet nuclei. In conclusion, I suggest that the radio activity in NGC 1275 is not determined only from the properties of circumnuclear gas, but it might be also related to the nature of the central engine. 
   The studies of NGC 5793 began with the detection of water maser emission toward the center using the 45 m telescope. The maser emission is symmetrically offset from the systemic velocity and could be inferred to arise in a rotating molecular disk by analogy with NGC 4258. VLBA observations were then conducted to search for a parsec-scale maser disk. The maser spots were found to be offset from the continuum peak by ～ 3 pc with an alignment between position angles of nuclear continuum jet. It is likely that maser emission originates in a molecular cloud foreground to the jet, and that amplifies the radio jet in the background. In addition to maser studies, we made VLBA 18-cm observations to search for OH absorption, which revealed that there exists compact OH gas distribution about 5 pc from the radio nucleus, showing a velocity gradient along the axis of the galactic disk on a larger scale. The sense of the OH velocity field differs from that of the kiloparsec-scale CO disk which I imaged using NMA. This suggests that the compact OH absorbing gas cloud might trace the circumnuclear molecular gas with kinematical motion on parsec scale. Thus, a series of parsec-scale images of NGC 5793 revealed a variety of molecular gas distribution in the circumnuclear region of this AGN., application/pdf, 総研大甲第385号},
 title = {High-Resolution Interferometric Study of Circumnuclear Gas in Radio-Active Galaxies},
 year = {}
}