Testing the (generalized) Chaplygin gas model with the lookback time-redshift data

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 <= A(c) <= 0.82 and 0.59 <= h <= 0.65 for the CG model, and 0.67 <= A(s) <= 0.89 and -0.29 <= alpha <= 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.