Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...530..207w&link_type=abstract
The Astrophysical Journal, Volume 530, Issue 1, pp. 207-212.
Astronomy and Astrophysics
Astronomy
8
Galaxies: Individual: Ngc Number: Ngc 4258, Galaxies: Kinematics And Dynamics, Galaxies: Nuclei, Masers
Scientific paper
The distribution in angle and frequency of unsaturated maser radiation in the plane of a thin Keplerian disk is treated. Calculations are performed to relate the observed flux densities to the intrinsic properties of the maser features. An application is the interpretation of the high-velocity, 22 GHz masing features of the disk around the black hole at the nucleus of the galaxy NGC 4258. In contrast to other assessments, the mean intensity that is inferred for the radiation within these features leads to (at most) only weak maser saturation, with a rate for stimulated emission that probably is about 0.1 s-1. This rate is consistent with the observed spectral line breadths of these features which are only compatible with rates for stimulated emission that are less than about 1 s-1. Certain approximations can be made in the calculations because the Keplerian velocity of the disk in NGC 4258 is much greater than the thermal velocity of the molecules. A simple expression is then obtained to relate the degree of saturation of the maser to the observed maser intensity.
Watson William D.
Wyld H. W.
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