Gravitational redshift in the NGC 4258 disk?

The recent observations of high-velocity maser emissions in NGC 4258 by Myoshi et al provide strong evidence for a central object of mass 3.6 10**7 solar masses in the nucleus of this galaxy based on a kinematic argument. However, they should allow an independent determination of the central object mass via gravitational redshift. We briefly discuss the size of the effect, and show that it should be detected in a more detailed analysis of the data.