When Did Cosmic Acceleration Start ?
Abstract
A precise determination, and comparison, of the epoch of the onset of cosmic acceleration, at redshift zacc, and of dark energy domination, at zeq, provides an interesting measure with which to parameterize dark energy models. By combining several cosmological datasets we place constraints on the redshift and age of cosmological acceleration. For a Lambda-CDM model, we find the constraint zacc=0.760.10 at 95% c.l., occurring 6.70.4 Gyrs ago. Allowing a constant equation of state but different from -1 changes the constraints to zacc=0.810.12 (6.90.5 Gyrs ago) and zeq=0.480.14(4.90.9 Gyrs ago), while dynamical models markedly increase the error on the constraints with zacc=0.810.30 (6.81.4 Gyrs ago) and zeq=0.440.20 (4.51.0 Gyrs ago). Unified dark energy models as Silent Quartessence yield: zacc=0.800.16 (6.80.6 Gyrs ago).
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