Comparing the VGCG model as the unification of dark sectors with observations

Current observations indicate that 95% of the energy density in the universe is the unknown dark component. The dark component is considered composed of two fluids: dark matter and dark energy. Or it is a mixture of these two dark components, i.e., one can consider it an exotic unknown dark fluid. With this consideration, the variable generalized Chaplygin gas (VGCG) model is studied with not dividing the unknown fluid into dark matter and dark energy parts in this paper. By using the Markov Chain Monte Carlo method, the VGCG model as the unification of dark sectors is constrained, and the constraint results on the VGCG model parameters are, n = 0.00057 (-0.0006-0.0006) (+0.0001+0.0009) , alpha = 0.0015 (-0.0015-0.0015) (+0.0003+0.0017) and B (s) = 0.778 (-0.016-0.035) (+0.016+0.030) , obtained by the cosmic microwave background data from the 7-year WMAP full data points, the baryon acoustic oscillation data from Sloan Digital Sky Survey (SDSS) and 2-degree Field Galaxy Redshift (2dFGRS) survey, and the Union2 type Ia supernova data with systematic errors. At last, according to the evolution of deceleration parameter it is shown that an expanded universe from deceleration to acceleration can be obtained in VGCG cosmology.