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 \pm 0.01 , k _ { 0 } = 0.09 ^ { +0.04 } _ { -0.03 } , \alpha = 1.8 ^ { +7.4 } _ { -0.7 } ( the best-fit values of the parameters ) and z _ { q = 0 } \sim 0.47 - 0.51 ( the transitional redshift ) for GTF as dark energy component only ; k _ { 0 } = 0.21 ^ { +0.20 } _ { -0.18 } , \alpha = 0.57 \pm 0.01 and z _ { q = 0 } \sim 0.49 - 0.68 for GTF as 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 test with independent H ( z ) data , we find 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 dark energy component , the fluctuations of matter density is consistent with the growth of linear density perturbations .
For GTF unified dark matter , the growth of GTF density fluctuations grow more slowly for a \rightarrow 1 , meaning GTF do not behave as classical \Lambda CDM scenarios .