2007A&A...467..421D

Dark energy is the invisible fuel that seems to drive the current acceleration of the Universe. Its presence, which is inferred from an impressive convergence of high-quality observational results along with some sucessful theoretical predictions, is also supported by the current estimates of the age of the Universe from dating of local and high-z objects. In this work we study observational constraints on the dark energy equation of state (w) from lookback time measurements of high-z galaxies, as recently published by the Gemini Deep Deep Survey (GDDS). To build up our lookback time sample from these observations we use 8 high-z galaxies in the redshift interval 1.3≤z≤2.2 and assume the total expanding age of the Universe to be t₀^obs=13.6^+0.4_–0.3Gyr, as obtained from current cosmic microwave background data. We show that these age measurements are compatible with values of w close to -1, although there is still space for quintessence (w>-1) and phantom (w←1) behaviors. To break possible degeneracies in the Ω_m-w plane, we also discuss the bounds on this parametric space when GDDS lookback time measurements are combined with the most recent SNe Ia, CMB, and LSS data.