We combine recent measurements of Cosmic Microwave Background Anisotropies , Supernovae luminosity distances and Baryonic Acoustic Oscillations to derive constraints on the dark energy equation of state w in the redshift range 0 < z < 2 , using a principal components approach .
We find no significant deviations from the expectations of a cosmological constant .
However , combining the datasets we find slight indication for w < -1 at low redshift , thus highlighting how these datasets prefer a non-constant w .
Nevertheless the cosmological constant is still in agreement with these observations , while we find that some classes of alternative models may be in tension with the inferred w ( z ) behaviour .