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, Λ, 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_∥, <b>k_⊥</b>), 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 Λ 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 Λr(z) results, and inconsistent with a Ω_Λ= 0 flat cosmology at over 95 per cent confidence.