EVIDENCE FOR DARK-MATTER IN MG-1654+134

The radio ring lens MG 1654 + 134 strongly constrains the structure and mass of the 19 mag lens galaxy at its center. The best-fit effective radius for a de Vaucouleurs model of the lens galaxy is R(e) = 2''.0 (1''.5 < R(e) < 3''.0) marginally consistent with fits to the observed lens galaxy. The B band mass-to-light ratio interior to the ring that the galaxy would have today is (M/L)(B) = (20.4 +/- 2.8)(f(e)/1.4)h, where a passively evolving early type galaxy fades by a factor of f(e) similar or equal to 1.4 between the lens redshift and the present. This (M/L)(B) is inconsistent with stellar dynamical models of nearby ellipticals, but it is consistent with estimates from the statistics of gravitational lens numbers and separations. Isothermal models fit the ring with a halo velocity dispersion of sigma(DM) = (216 +/- 2) km s(-1), consistent with the fundamental plane, the stellar dynamics of ellipticals in dark matter halos [predicted dispersion (212 +/- 12)(f(e)/1.4)(-0.29) km s(-1)], and the statistics of gravitational lenses. This strongly supports the conclusion from lens statistics that early type galaxies do not have constant mass-to-light ratios even on scales comparable to the effective radius. Density distributions with rho proportional to (r(2) + s(2))((alpha) (-) (3)/2) fit the data only in the restricted range 0.9 less than or similar to alpha less than or similar to 1.1 where alpha = 1 is an isothermal model. Centrally concentrated models such as the Plummer or modified Hubble models require large, finite core radii (800 h(-1) and 600 h(-1) pc, respectively) but fail to fit the structure of the ring. Isothermal models only have upper limits of order 100 h(-1) pc on the core radius. The major axis of the mass distribution is 7 degrees +/- 10 degrees from the major axis of the luminosity distribution. The models clearly distinguish between different angular structures for the lens model, and a quadrupole expansion of an ellipsoidal density distribution fits the data better than a similar monopole in an external shear.