Gravitational lenses as cosmic rulers: Ωₘ, ΩΛ from time delays and velocity dispersions

We show that a cosmic standard ruler can be constructed from the joint measurement of the time delay, , between gravitationally lensed quasar images and the velocity dispersion, σ, of the lensing galaxy. This is specifically shown, for a singular isothermal sphere lens, , where DOL is the angular diameter distance to the lens. Using MCMC simulations we illustrate the constraints set in the plane from future observations.