Thawing versus tracker behaviour: observational evidence

Currently there exist a variety of scalar field models that attempt to explain the late-time acceleration of the Universe. This includes the standard canonical and non-canonical scalar field models together with the recently proposed Galileon scalar field models. One can divide all these scalar field models into two broad categories, namely thawing and tracker classes. In this work we investigate the evidence for these models from presently available observational data using the Bayesian approach. We use the generalized Chaplygin gas (GCG) parametrization for the dark energy equation of state (EoS), as it exhibits both thawer- and tracker-like behaviour for different values of the parameters. Subsequently we use Type Ia supernova (SnIa) measurements, recent measurements of the Hubble parameter at different redshifts (H(z)), measurements of the look-back time at different redshifts (Lookback), measurements of the linear growth factor in large-scale structure (GR) from various redshift surveys and finally measurement of the anisotropies in the cosmic microwave background radiation by WMAP-7 observations. The analysis of data from SN+ H(z)+Lookback does not favour either tracker or thawer classes. Inclusion of data from GR+WMAP-7 favours the thawer class of models if one assumes the dark energy to be a smooth component. If we consider dark energy perturbations, however, both tracker and thawer types of models are equally favoured by the data.