2003ApJ...583...49K

In standard cold dark matter (CDM) halo models, the time delay of a gravitational lens is determined by the cold baryon mass fraction, f_b=Ω_b,cold/Ω₀, of the visible galaxy relative to the overall halo. The observed time delays in PG 1115+080, SBS 1520+530, B1600+434, and HE 2149-2745 give Hubble constants consistent with the Hubble Space Telescope Key Project value of H₀=72±8 km.s^–1.Mpc^–1 only if f_b≳0.2 (one-sided 68% confidence), which is larger than the upper bound of f_b,max=Ω_b/Ω₀=0.15±0.05 estimated from the cosmic microwave background. If all available baryons cool and f_b=f_b,max, then the time delays imply H₀=65±6 km.s^–1.Mpc^–1 (95% confidence). If local inventories of cold baryons, f_b≃0.013/h₇₀, are correct, then H₀=52±6 km.s^–1 .Mpc^–1 and the halo parameters closely match isothermal mass models. Isothermal models are also consistent with strong and weak lens studies, stellar dynamics, and X-ray observations on these scales, while significantly more centrally concentrated models are not. There is a conflict between gravitational lens time delays, the local distance scale, and standard CDM halo models.