Constraints on H_0 from the Central Velocity Dispersions of Lens Galaxies

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Abstract
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 h_4 observed in nearby galaxies for 0 < R < 2 R_eff. 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-sigma limits on the Hubble constant of H_0 = (66 +13/-20) km/s/Mpc. For PG 1115+080, we find that the central dispersion is consistent with the singular isothermal lens model, for which H_0 = (44 +/- 4) km/s/Mpc, and formally inconsistent with the constant mass-to-light ratio model, for which H_0 = (65 +/- 5) km/s/Mpc, at the 1.5-sigma confidence level.

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