The Lensing Galaxy in MG1549+3047

We have measured a velocity dispersion for the foreground galaxy in this gravitationally lensed system. Our dispersion confirms the prediction from lens models, provided that the source is distant enough ($z_{{}_S}>0.2$). Current interpretations of lensing statistics depend sensitively on how the optical and mass dispersions are related. For $z_{{}_S}>0.5$, our observations favor ${\sigma }_{mass}\mathrm{/}{\sigma }_{opt}\simeq 1$, but our uncertainties prevent us from clearly distinguishing between dynamical models. We could not obtain a unique mass profile from lensing constraints, but models with a constant mass-to-light ratio are possible. We also found unusual rotation in the lensing galaxy, and confirmed its redshift.