Observational constraints on the generalized Chaplygin gas model

The generalized Chaplygin gas model with parameter space α>−1 is studied in this paper. Some reasonable physical constraints are added to justify the use of the larger parameter space. The constraints ensure that the present sound speed of the total system . The type Ia supernova data and the age data of some clusters are then used to fit the model. We find that the parameters have bimodal distributions. For the generalized Chaplygin gas model, we also find that fewer free parameters fit the data better. The best fit model is the spatially flat model with baryons. The best fit parameters are: Ω m 0 = 0.044, w c 0 = −0.881 and α = 1.57. By using the best fit parameters, we find that the transition redshift is z T = 0.395.