A determination of H0 with the class gravitational lens B1608+656.: II.: Mass models and the Hubble constant from lensing

We present mass models of the four-image gravitational lens system B1608 + 656, based on information obtained through VLBA imaging, VLA monitoring, and Hubble Space Telescope (HST) WFPC2 and NICMOS imaging. We have determined a mass model for the lens galaxies that reproduces (1) all image positions within the observational errors, (2) two out of three flux-density ratios within about 10% from the observed ratios, and (3) the model time delays within 1% from their observed values, given our best estimate of the Hubble parameter. Using the time delays determined in a companion paper, we also find that the best isothermal mass model gives H-0 = 59(-6)(+7) km s(-1) Mpc(-1) for Omega(m) = 1 and Omega(Lambda) = 0.0, or H-0 = (65-63)(-6)(+7) km s(-1) Mpc(-1) for Omega(m) = 0.3 and Omega(Lambda) = 0.0-0.7. The statistical errors indicate the 95.4% (2 sigma) confidence interval. A systematic error of +/-15 km s(-1) Mpc(-1) is estimated from a 20% (1 sigma) uncertainty in the steepness of radial mass profile. This cosmological determination of H-0 agrees well with determinations from three other gravitational lens systems (i.e., B0218 + 357, Q0957 + 561, and PKS 1830-211), Type Ia supernovae, the Sunyaev-Zeldovich effect and local determinations. The current agreement on H-0-within the 1 sigma statistical errors-from four of five gravitational lens systems (1) emphasizes the reliability of its determination from isolated gravitational lens systems and (2) suggests that a close-to-isothermal mass profile can describe disk galaxies (e.g., B0218 + 357 and possibly PKS 1830-211), ellipticals (e.g., B1608 +/- 656), and central cluster ellipticals (e.g., 00957 + 561). The average of H-0 from B0218 + 357, Q0957 + 561, B1608 + 656, and PKS 1830-211, gives H-0(GL) = 69 +/- 7 km s(-1) Mpc(-1) for a flat universe with Omega(m) = 1 or H-0(GL) = 74 +/- 8 km s(-1) Mpc(-1) for Omega(m) = 0.3 and Omega(Lambda) = 0.0-0.7. When including PG 1115 + 080, these values decrease to 64 +/- 11 km s(-1) Mpc(-1) and 68 +/- 13 km s(-1) Mpc(-1), respectively. The errors are the estimated 2 a errors on the average. The Hubble parameter from gravitational lenses seems to agree best with local determinations of H-0 for a low-density universe, under the assumption that all lenses are nearly isothermal.