With large-scale homogeneity, the universe is locally inhomogeneous, clustering into stars, galaxies and larger structures. Such property is described by the smoothness parameter α which is defined as the proportion of matter in the form of intergalactic medium. If we consider the inhomogeneities over a small scale, there should be modifications of the cosmological distances compared to a homogenous model. Dyer and Roeder developed a second-order ordinary differential equation (D-R equation) that describes the angular diameter distance-redshift relation for inhomogeneous cosmological models. Furthermore, we may obtain the D-R equation for observational H(z) data (OHD). The density-parameter ΩM, the state of dark energy ω, and the smoothness-parameter α are constrained by a set of OHD in a spatially flat ΛCDM universe as well as a spatially flat XCDM universe. By using a χ2 minimization method, we get α = 0.81+0.19-0.20 and Ωm = 0.32 +0.12-0.06 at the 1σ confidence level. If we assume a Gaussian prior of ΩM = 0.26 ± 0.1, we get α = 0.93+0.07-0.19 and Ωm = 0.31 +0.06-0.05. For the XCDM model, α is constrained to α ≥ 0.80 but ω is weakly constrained around - 1, where ω describes the equation of state of the dark energy (pX = ωρX). We conclude that OHD constrains the smoothness parameter more effectively than the data of SNe Ia and compact radio sources.
CITATION STYLE
Yu, H. R., Lan, T., Wan, H. Y., Zhang, T. J., & Wang, B. Q. (2011). Constraints on smoothness parameter and dark energy using observational H(z) data. Research in Astronomy and Astrophysics, 11(2), 125–136. https://doi.org/10.1088/1674-4527/11/2/001
Mendeley helps you to discover research relevant for your work.