2001MNRAS.325.1097G

We calculate analytically and numerically the distance-redshift equation in perfect fluid quintessence models and give an accurate fit to the numerical solutions for all the values of the density parameter and the quintessence equation of state. Then we apply our solutions to the estimation of H₀ from multiple image time delays and find that the inclusion of quintessence modifies significantly the likelihood distribution of H₀, generally reducing the best estimate with respect to a pure cosmological constant. Marginalizing over the other parameters (Ω_m and the quintessence equation of state) we obtain H₀=71±6km.s^–1.Mpc^–1 for an empty beam and H₀=64±4km.s^–1.Mpc^–1 for a filled beam. These errors, however, do not take into account the uncertainty on the modelling of the lens. We also discuss the future prospects for distinguishing quintessence from a cosmological constant with time delays.