The 2dF QSO Redshift survey: XIII. A measurement of Λ from the quasi-stellar object power spectrum, PS(k∥, k⊥)

We report on measurements of the cosmological constant, A, and the redshift space distortion parameter β = Ω 0.6 m/b, based on an analysis of the quasi-stellar object (QSO) power spectrum parallel and perpendicular to the observer's line of sight, P S (k∥, k⊥), from the final catalogue of the Two-Degree Field (2dF) QSO Redshift Survey. We derive a joint Λ - β constraint from the geometric and redshift-space distortions in the power spectrum. By combining this result with a second constraint based on mass clustering evolution, we break this degeneracy and obtain strong constraints on both parameters. Assuming a flat (Ω m + Ω Λ = 1) cosmology and a A cosmology r(z) function to convert from redshift into comoving distance, we find best-fitting values of Ω Λ = 0.71 +0.09 -0.17 and β q (z ∼ 1.4) = 0.45 +0.09 -0.11. Assuming instead an Einstein-de Sitter cosmology r(z) we find that the best-fitting model obtained, with Ω Λ = 0.64 +0.11 -0.16 and β q (z ∼ 1.4) = 0.40 +0.09 -0.09, is consistent with the A r(z) results, and inconsistent with a Ω Λ = 0 flat cosmology at over 95 per cent confidence.