The Chaplygin gas ( CG ) and the generalized Chaplygin gas ( GCG ) models , proposed as candidates of the unified dark matter-dark energy ( UDME ) , are tested with the look-back time ( LT ) redshift data .
We find that the LT data only give a very weak constraint on the model parameter .
However , by combing the LT with the baryonic acoustic oscillation peak , we obtain , at the 95.4 \% confidence level , 0.68 \leq A _ { c } \leq 0.82 and 0.59 \leq h \leq 0.65 for the CG model , and 0.67 \leq A _ { s } \leq 0.89 and -0.29 \leq \alpha \leq 0.61 for the GCG model .
This shows that both the CG and the GCG are viable as a candidate of UDME .
Within the GCG model , we also find that the Chaplygin gas model ( \alpha = 1 ) is ruled out by these data at the 99.7 \% confidence level .