We determine the best-fit values and confidence limits for dynamical dark energy parameters together with other cosmological parameters on the basis of different datasets which include WMAP9 or Planck-2013 results on CMB anisotropy, BAO distance ratios from recent galaxy surveys, magnitude-redshift relations for distant SNe Ia from SNLS3 and Union2.1 samples and the HST determination of the Hubble constant. We use a Markov Chain Monte Carlo routine to map out the likelihood in the multi-dimensional parameter space. We show that the most precise determination of cosmological parameters with the narrowest confidence limits is obtained for the Planck{+}HST{+}BAO{+}SNLS3 dataset. The best-fit values and 2$sigma$ confidence limits for cosmological parameters in this case are $Omega_{de}=0.718pm0.022$, $w_0=-1.15^{+0.14}_{-0.16}$, $c_a^2=-1.15^{+0.02}_{-0.46}$, $Omega_bh^2=0.0220pm0.0005$, $Omega_{cdm}h^2=0.121pm0.004$, $h=0.713pm0.027$, $n_s=0.958^{+0.014}_{-0.010}$, $A_s=(2.215^{+0.093}_{-0.101})cdot10^{-9}$, $tau_{rei}=0.093^{+0.022}_{-0.028}$. For this dataset, the $Lambda$CDM model is just outside the 2$sigma$ confidence region, while for the dataset WMAP9{+}HST{+}BAO{+}SNLS3 the $Lambda$CDM model is only 1$sigma$ away from the best fit. The tension in the determination of some cosmological parameters on the basis of two CMB datasets WMAP9 and Planck-2013 is highlighted.
We analyze the possibility to distinguish between quintessence and phantom scalar field models of dark energy using observations of luminosity distance moduli of SNe Ia, CMB anisotropies and polarization, matter density perturbations and baryon acoustic oscillations. Among the present observations only Planck data on CMB anisotropy and SDSS DR9 data on baryon acoustic oscillations may be able to decide between quintessence or phantom scalar field models, however for each model a set of best-fit parameters exists, which matches all data with similar goodness of fit. We compare the relative differences of best-fit model predictions with observational uncertainties for each type of data and we show that the accuracy of SNe Ia luminosity distance data is far from the one necessary to distinguish these types of dark energy models, while the CMB data (WMAP, ACT, SPT and especially Planck) are close to being able to reliably distinguish them. Also an improvement of the large-scale structure data (future releses of SDSS BOSS and e.g. Euclid or BigBOSS) will enable us to surely decide between quintessence and phantom dark energy.
