Constraints on the unified dark energy - dark matter model from latest observational data

The generalized Chaplygin gas (GCG) is studied in this paper by using the latest observational data including 182 gold sample type Ia supernovae (Sne Ia) data, the ESSENCE Sne Ia data, the distance ratio from z = 0.35 to 1089 (the redshift of decoupling), the cosmic microwave background shift parameter and the Hubble parameter data. Our results rule out the standard Chaplygin gas model (alpha = 1) at the 99.7% confidence level, but allow for the lambda CDM model (alpha = 0) at the 68.3% confidence level. At a 95.4% confidence level, we obtain w = - 0.74(-0.09)(+0.10) and alpha = - 0.14(-0.19)(+0.30) . In addition, we find that the phase transition from deceleration to acceleration occurs at redshift z(q) = 0 similar to 0.78 - 0.89 at a 1 sigma confidence level for the GCG model.