HUBBLE PARAMETER MEASUREMENT CONSTRAINTS ON THE COSMOLOGICAL DECELERATION-ACCELERATION TRANSITION REDSHIFT

We compile a list of 28 independent measurements of the Hubble parameter between redshifts 0.07 <= z <= 2.3 and use this to place constraints on model parameters of constant and time-evolving dark energy cosmologies. These H(z) measurements by themselves require a currently accelerating cosmological expansion at about, or better than, 3 sigma confidence. The mean and standard deviation of the six best-fit model deceleration-acceleration transition redshifts (for the three cosmological models and two Hubble constant priors we consider) are z(da) = 0.74 +/- 0.05, in good agreement with the recent Busca et al. determination of z(da) = 0.82 +/- 0.08 based on 11 H(z) measurements between redshifts 0.2 <= z <= 2.3, almost entirely from baryon-acoustic-oscillation-like data.