Observational constraints on dark energy model

The recent observations support that our Universe is flat and expanding with acceleration. We analyze a general class of quintessence models by using the recent type Ia supernova and the first year Wilkinson Microwave Anisotropy Probe (WMAP) observations. For a flat universe dominated by a dark energy with constant ω which is a special case of the general model, we find that Ωm0 = 0.30 +0.06 −0.08 and ωQ ≤ −0.82, and the turnaround redshift zT when the universe switched from the deceleration phase to the acceleration phase is zT = 0.65. For the general model, we find that Ωm0 ∼ 0.3, ωQ0 ∼ −1.0, β ∼ 0.5 and zT ∼ 0.67. A model independent polynomial parameterization of dark energy is also considered, the best fit model gives Ωm0 = 0.40±0.14, ωQ0 = −1.4 and zT = 0.37.