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)/sigma(opt)similar or equal to 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. (C) 1996 American Astronomical Society.