Astrophysical maser radiation from Keplerian disks near active galactic nuclei

Calculations are performed that are relevant for understanding maser radiation emerging from gaseous disks at the nuclei of active galaxies. In at least one galaxy (NGC 4258), such maser radiation is observed and arises from a disk around a presumed massive black hole. The heating, cooling, and excitation mechanisms necessary for creating the physical conditions and pumping for the masing are investigated. The emergent spectra are first calculated for a smooth, Keplerian disk including the effects of radiative saturation. To understand the irregularities in space and frequency in the observations of NGC 4258, calculations are then performed with idealized turbulent velocities superimposed on the Keplerian velocity of the disk. These turbulent velocities are created by statistical sampling from a Kolmogorov-like distribution. In addition to rays of radiation parallel to the plane of the disk, rays inclined at a 7° angle (that indicated for NGC 4258) to the plane of the disk are considered. Within the context of this turbulent disk model, calculations for the time dependence of the low- and high-velocity masing features are performed and compared with observed variations from NGC 4258.U of I Onlythesi