西佛一型星系NGC 1097之中心CO氣體性質研究

Abstract

The first 12CO(J=2-1) interferometric image of the Seyfert 1 galaxy NGC 1097 is presented in this work. The 12CO(J=2-1) map shows a strong nuclear concentration coincident with the Seyfert nucleus, and a molecular ring corresponding to the starburst ring shown in optical images. The 12CO(J=2-1)/(J=1-0) intensity ratio of the nuclear concentration is up to 1.95+-0.14 and it suggests that the physical condition of the central molecular gas is warm (>250 K) and dense (~10^4 cm^-3). A velocity map shows that the nuclear molecular gas is rotating with the molecular ring in the same sense, while its velocity gradient is much steeper than that of the ring. This steep velocity gradient at the central molecular gas can be interpreted as a highly-inclined disk or low-inclined disk with small radius. In the case of the highly-inclined disk, it could be clumpy, or warped, or with large truncation between AGN and torus to see through the AGN. In the case of the low-inclined disk, its size has to be small enough to explain the steep velocity gradient. The molecular ring is a site of starburst judged by a physical conditions relatively warmer and denser than the GMCs, and an analysis of Toomre instability suggests star formation in the ring. The origin of the ring may be attributed to Lindblad resonance, which is suggested by the hydrodynamical simulation.