HUBBLE PARAMETER MEASUREMENT CONSTRAINTS ON DARK ENERGY

Abstract

We use 21 Hubble parameter versus redshift data points, from Gazta\\~{n}aga et\nal. (2009), Stern et al. (2010), and Moresco et al. (2012), to place\nconstraints on model parameters of constant and time-evolving dark energy\ncosmologies. This is the largest set of H(z) data considered to date. The\ninclusion of the 8 new Moresco et al. (2012) measurements results in H(z)\nconstraints more restrictive than those derived by Chen & Ratra (2011b). These\nconstraints are now almost as restrictive as those that follow from current\nType Ia supernova (SNIa) apparent magnitude versus redshift data (Suzuki et al.\n2012), which now more carefully account for systematic uncertainties. This is a\nremarkable result. We emphasize however that SNIa data have been studied for a\nlonger time than the H(z) data, possibly resulting in a better estimate of\npotential systematic errors in the SNIa case. A joint analysis of the H(z),\nbaryon acoustic oscillation peak length scale, and SNIa data favors a\nspatially-flat cosmological model currently dominated by a time-independent\ncosmological constant but does not exclude slowly-evolving dark energy.\n