Constraints on H0 from the Central Velocity Dispersions of Lens Galaxies

We employ Schwarzschild’s method of orbit modeling to constrain the mass profiles of the central lens galaxies in 0957+561 and PG 1115+080. We combine the measured central projected stellar velocity dispersions of these galaxies with the self-similar radial profiles of the rms velocity and of the Gauss-Hermite moment h4 observed in nearby galaxies for 0 <∼ R <∼ 2Reff . For 0957+561, we find a 15% uncertainty in the galaxy mass, and in combination with weak lensing studies of the system, we find formal 2-σ limits on the Hubble constant of H0 = 66 +13 −20 km s −1 Mpc−1. For PG 1115+080, we find that the central dispersion is consistent with the singular isothermal lens model, for which H0 = 44 ± 4 km s−1 Mpc−1, and formally inconsistent with the constant mass-to-light ratio model, for which H0 = 65±5 km s−1 Mpc−1, at the 1.5-σ confidence level. Subject headings: galaxies: elliptical and lenticular, cD — galaxies: structure — galaxies: fundamental parameters — galaxies: kinematics and dynamics — gravitational lensing — quasars: individual (0957+561) — quasars: individual (PG 1115+080) — distance scale — dark matter