Age constraints on the cosmic equation of state

¹ Observatório Nacional, Rua Gal. José Cristino 77, 20921-400 Rio de Janeiro, RJ, Brasil e-mail: [aldinez;alcaniz]@on.br
² Deen Dayal Updhyaya College, University of Delhi, Delhi 110 015, India e-mail: deepak@physics.du.ac.in
³ Miranda House, University of Delhi, Delhi 110007, India

Received: 24 October 2006
Accepted: 9 January 2007

Abstract

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 and assume the total expanding age of the Universe to be  Gyr, 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 () and phantom () behaviors. To break possible degeneracies in the  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.