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 la supernova and the first year Wilkinson Microwave Anisotropy Probe (WMAP) observations. For a flat universe dominated by a dark energy with constant W which is a special case of the general model, we find that Omega(m0) = 0.30(-0.08)(+0.06) and omega(Q) <= -0.82, and the turnaround redshift ZT when the universe switched from the deceleration phase to the acceleration phase is z(T) = 0.65. For the general model, we find that Omega(m0) similar to 0.3, omega(Q0) similar to -1.0, beta similar to 0.5 and z(T) similar to 0.67. A model independent polynomial parametrization of dark energy is also considered, the best fit model gives Omega(m0) = 0.40 +/- 0.14, omega(Q0) = -1.4 and z(T) = 0.37.