Hubble Parameter Measurement Constraints on the Redshift of the Deceleration–acceleration Transition, Dynamical Dark Energy, and Space Curvature

We compile an updated list of 38 measurements of the Hubble parameter H ( z ) between redshifts 0.07 ≤ z ≤ 2.36 and use them to place constraints on model parameters of constant and time-varying dark energy cosmological models, both spatially flat and curved. We use five models to measure the redshift of the cosmological deceleration–acceleration transition, z da , from these H ( z ) data. Within the error bars, the measured z da are insensitive to the model used, depending only on the value assumed for the Hubble constant H 0 . The weighted mean of our measurements is z da = 0.72 ± 0.05 (0.84 ± 0.03) for H 0 = 68 ± 2.8 (73.24 ± 1.74) km s −1 Mpc −1 and should provide a reasonably model-independent estimate of this cosmological parameter. The H ( z ) data are consistent with the standard spatially flat ΛCDM cosmological model but do not rule out nonflat models or dynamical dark energy models.