Direct Determination of the Kinematics of the Universe and Properties of the Dark Energy as Functions of Redshift

Understanding of the nature of dark energy, which appears to drive the expansion of the universe, is one of the central problems of physical cosmology today. In an earlier paper [Daly & Djorgovski (2003)] we proposed a novel method to determine the expansion rate E(z) and the deceleration parameter q(z) in a largely model-independent way, directly from the data on coordinate distances y(z). Here we expand this methodology to include measurements of the pressure of dark energy p(z), its normalized energy density fraction f(z), and the equation of state parameter w(z). We then apply this methodology to a new, combined data set of distances to supernovae and radio galaxies. In evaluating E(z) and q(z), we make only the assumptions that the FRW metric applies, and that the universe is spatially flat (an assumption strongly supported by modern CMBR measurements). The determinations of E(z) and q(z) are independent of any theory of gravity. For evaluations of p(z), f(z) and w(z), a theory of gravity must be adopted, and General Relativity is assumed here. No a priori assumptions regarding the properties or redshift evolution of the dark energy are needed. We obtain trends for y(z) and E(z) which are fully consistent with the standard Friedmann-Lemaitre concordance cosmology with Ω0 = 0.3 and Λ0 = 0.7.