The internal structure of the lens PG1115+080: breaking degeneracies in the value of the Hubble Constant
Abstract
We combine lensing, stellar kinematic and mass-to-light ratio constraints to build a two-component (luminous plus dark) mass model of the early-type lens galaxy in PG1115+080. We find a total mass density profile steeper than r-2, effectively rho r-gamma' with gamma'=2.35+-0.1+-0.05 (random + systematic). The stellar mass fraction is f*=0.67(+0.20/-0.25)+-0.03 inside the Einstein Radius (RE 1.2 effective radii). The dynamical mass model breaks the degeneracies in the mass profile of the lens galaxy and allows us to obtain a value of the Hubble Constant that is no longer dominated by systematic errors: H0=59(+12/-7)+-3 km/s/Mpc (68 percent C.L.; Omegam=0.3, OmegaL=0.7). The offset of PG1115+080 from the Fundamental Plane might indicate deviations from homology of the mass profile of some early-type galaxies.
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