Tangential Large Scale Structure as a Standard Ruler: Curvature Parameters from Quasars

Abstract

Several observational analyses suggest that matter is spatially structured at $\approx 130h^{-1}Mpc$ at low redshifts. This peak in the power spectrum provides a standard ruler in comoving space which can be used to compare the local geometry at high and low redshifts, thereby constraining the curvature parameters. It is shown here that this power spectrum peak is present in the observed quasar distribution at $z\sim 2$: qualitatively, via wedge diagrams which clearly show a void-like structure, and quantitatively, via one-dimensional Fourier analysis of the quasars' tangential distribution. The sample studied here contains 812 quasars. The method produces strong constraints (68% confidence limits) on the density parameter $Ω_0$ and weaker constraints on the cosmological constant $λ_0$, which can be expressed by the relation $ Ω_0 = (0.24 \pm0.15) + (0.10\pm0.08) λ_0 $. Independently of $λ_0$ (in the range $λ_0 \in [0,1]$), the constraint is $0.1 < Ω_0 < 0.45$. Combination of the present results with SN Type Ia results yields $Ω_0 = (0.30\pm0.11) + (0.57\pm0.11) (λ_0-0.7),$ $0.55 < λ_0 < 0.95,$ (68% confidence limits). This strongly supports the possibility that the observable universe satisfies a nearly flat, perturbed Friedmann-Lema\^ıtre-Robertson-Walker model, independently of any cosmic microwave background observations.