EVIDENCE FROM MASERS FOR A RAPIDLY ROTATING-DISK AT THE NUCLEUS OF NGC-4258

We demonstrate how maser emission from a rapidly rotating, thin Keplerian disk viewed edge-on can reproduce the general features of the observed 22 GHz radiation from the nucleus of NGC 4258, including the high-velocity satellites that are Doppler shifted by nearly +/- 1000 km s-1 from the central emission. Newly reported data about variations in time and space for the Doppler shifts of the central emission features fit especially well into a disk interpretation. We point out that their ratio gives a velocity of 700 km s-1 for the rotation at the outer edge of the masing ring-a value that is essentially the same as the rotational velocity inferred from the Doppler shifts of the high-velocity satellites. The radius of the masing ring is 0.1 pc and the central mass at the nucleus of NGC 4258 about which the disk rotates is then 10(7) M..