Constraints on the generalized tachyon field models from latest observational data

We consider constraints on generalized tachyon field (GTF) models from latest observational data (including 182 gold SNIa data, the shift parameter, and the acoustic scale). We obtain at 68.3% confidence level Omega m = 0.37 +/- 0.01, k(0) = 0.09(-0.03)(+0.04), alpha = 1.8(-0.7)(+7.4) (the best fit values of the parameters) and z(q=0) similar to 0.47 - 0.51 (the transitional redshift) for GTF as the dark energy component only; k(0) = 0.21(-0.18)(+0.20), alpha = 0.57 +/- 0.01 and z(q=0) similar to 0.49-0.68 for GTF as the unification of dark energy and dark matter. In both cases, GTF evolves like dark matter in the early universe. By applying model- comparison statistics and testing with independent H(z) data, we find that the GTF dark energy scenario is favored over the Lambda CDM model, and the Lambda CDM model is favored over GTF unified dark matter by the combined data. For GTF as the dark energy component, the fluctuations of matter density are consistent with the growth of linear density perturbations. For GTF unified dark matter, the growth of GTF density fluctuations goes more slowly for a --> 1, meaning that GTF does not behave as classical Lambda CDM scenarios.