The generalized Chaplygin gas model ( GCGM ) contains 5 free parameters that must be constrained using the different observational data .
These parameters are : the Hubble constant H _ { 0 } , the parameter \bar { A } related to the sound velocity , the equation of state parameter \alpha , the curvature parameter \Omega _ { k 0 } , and the Chaplygin gas density parameter \Omega _ { c 0 } .
The pressureless matter parameter \Omega _ { m 0 } may be obtained as a dependent quantity .
Here , these parameters are constrained through the type Ia supernovae data .
The “ gold sample ” of 157 supernovae data is used .
Negative and large positive values for \alpha are taken into account .
The analysis is made by employing the Bayesian statistics and the prediction for each parameter is obtained by marginalizing on the remained ones .
This procedure leads to the following predictions : \alpha = -0.75 ^ { +4.04 } _ { -0.24 } , H _ { 0 } = 65.00 ^ { +1.77 } _ { -1.75 } , \Omega _ { k 0 } = -0.77 ^ { +1.14 } _ { -5.94 } , \Omega _ { m 0 } = 0.00 ^ { +1.95 } _ { -0.00 } , \Omega _ { c 0 } = 1.36 ^ { +5.36 } _ { -0.85 } , \bar { A } = 1.000 ^ { +0.000 } _ { -0.534 } .
Through the same analysis the specific case of the ordinary Chaplygin gas model ( CGM ) , for which \alpha = 1 , is studied .
In this case , there are now four free parameters and the predictions for them are : H _ { 0 } = 65.01 ^ { +1.81 } _ { -1.71 } , \Omega _ { k 0 } = -2.73 ^ { +1.53 } _ { -0.97 } , \Omega _ { m 0 } = 0.00 ^ { +1.22 } _ { -0.00 } , \Omega _ { c 0 } = 1.34 ^ { +0.94 } _ { -0.70 } , \bar { A } = 1.000 ^ { +0.000 } _ { -0.270 } .
To complete the analysis the \Lambda CDM , with its three free parameters , is considered .
For all these models , particular cases are considered where one or two parameters are fixed .
The age of the Universe , the deceleration parameter and the moment the Universe begins to accelerate are also evaluated .
The quartessence scenario , that unifies the description for dark matter and dark energy , is favoured .
A closed ( and in some cases a flat ) and accelerating Universe is also preferred .
The CGM case \alpha = 1 is far from been ruled out , and it is even preferred in some particular cases .
In most of the cases the \Lambda CDM is disfavoured with respect to GCGM and CGM .