The type Ia supernovae ( SNe Ia ) observational data are used to estimate the parameters of a cosmological model with cold dark matter and the generalized Chaplygin gas model ( GCGM ) .
The GCGM depends essentially on five parameters : the Hubble constant , the parameter \bar { A } related to the velocity of the sound , the equation of state parameter \alpha , the curvature of the Universe and the fraction density of the generalized Chaplygin gas ( or the cold dark matter ) .
The parameter \alpha is allowed to take negative values and to be greater than 1 .
The Bayesian parameter estimation yields \alpha = -0.86 ^ { +6.01 } _ { -0.15 } , H _ { 0 } = 62.0 ^ { +1.32 } _ { -1.42 } km / Mpc . s , \Omega _ { k 0 } = -1.26 _ { -1.42 } ^ { +1.32 } , \Omega _ { m 0 } = 0.00 ^ { +0.86 } _ { -0.00 } , \Omega _ { c 0 } = 1.39 ^ { +1.21 } _ { -1.25 } , \bar { A } = 1.00 ^ { +0.00 } _ { -0.39 } , t _ { 0 } = 15.3 ^ { +4.2 } _ { -3.2 } and q _ { 0 } = -0.80 ^ { +0.86 } _ { -0.62 } , where t _ { 0 } is the age of the Universe and q _ { 0 } is the value of the deceleration parameter today .
Our results indicate that a Universe completely dominated by the generalized Chaplygin gas is favoured , what reinforces the idea that the this gas may unify the description for dark matter and dark energy , at least as the SNe Ia data is concerned .
A closed and accelerating Universe is also favoured .
The traditional Chaplygin gas model ( CGM ) , \alpha = 1 is not ruled out , even if it does not give the best-fitting .
Particular cases with four or three independent free parameters are also analysed .