Year: 2011
Type: article
Abstract: 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 χ 2 minimization method, we get α = 0.81 +0.19 −0.20 and Ω M = 0.32 +0.12 −0.06 at the 1σ confidence level. If we assume a Gaussian prior of Ω M = 0.26 ± 0.1, we get α = 0.93 +0.07 −0.19 and Ω M = 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 ( p X = ωρ X ). We conclude that OHD constrains the smoothness parameter more effectively than the data of SNe Ia and compact radio sources.
Authors: Hao-Ran Yu, Tian Lan, Hao-Yi Wan, Tong-Jie Zhang, Bao-Quan Wang
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W1964873031