An Accretion-Disk Model with Cooling through Molecular Lines

作者：Kai Takashi^*; Baba Tamon; Arai Kenzo

来源：Publications of the Astronomical Society of Japan, 2012, 64(4): 68.

DOI：10.1093/pasj/64.4.68

• accretion, accretion disks
• galaxies: active
• galaxies: individual (NGC 4258)
• masers

We investigated an accretion-disk model with line-cooling of H2O and CO. The abundances of molecules were calculated numerically by the chemical reaction network, along with the structure of the disk. It was found that, when the model is applied to the Keplerian disk observed in the nucleus of NGC 4258, the temperature is T similar or equal to 400-500 K, the number density of molecular hydrogen is n(H-2) 10(7)-10(9)cm(-3), and the fractional abundance of H2O amounts to 10(-3) in the maser emitting region for the mass-accretion rate M similar or equal to 10(-6)-10(-7) M-circle dot yr(-1) and the viscosity parameter alpha = 0.1. In the outer region, the disk is both geometrically and optically thin, the drift time is at most 1 Gyr, self-gravity of the disk can be neglected, and irradiation from the inner disk is of also a negligible effect. The Toomre Q parameter is greater than unity, leading the disk to be gravitationally stable. It was also found that these physical circumstances cannot be achieved in the optically thick model cooled by blackbody radiation.

• 出版日期2012-8-25