Excitation for Masing by Water in X-irradiated Environments at the Nuclei of Active Galaxies

摘要

Recent calculations have demonstrated that the absorption of infrared, spectral line radiation by dust grains can increase significantly the pumping of the 22 GHz water masers under conditions that may be appropriate for the circumnuclear environment of active galaxies. As a result, improved agreement with the observed maser luminosities is achieved. A key ingredient is a significant difference between the temperatures of the gas and the grains, a difference that is expected in the presence of irradiation by X-rays. In our own galaxy, strong maser emission is observed also for a number of other transitions of the water molecule at higher frequencies. Calculations are presented here to delineate in some detail the maser luminosities that can be expected for both these and the 22 GHz transition when the influence of dust grains is included.