Large-scale clustering of sloan digital sky survey quasars: Impact of the baryon density and the cosmological constant

We report on the first result from the clustering analysis of SDSS quasars. We computed the two-point correlation function (2PCF) of SDSS quasars in redshift space at 8 h^-1 Mpc < s < 500 h^-1 Mpc, with particular attention to its baryonic signature. Our sample consisted of 19986 quasars extracted from the SDSS Data Release 4. The redshift range of the sample is 0.72 ≤ z ≤ 2.24 (the mean redshift is z̄ = 1.46) and the reddening-corrected i-band apparent magnitude range is 15.0 ≤ m _i.rc ≤ 19.1. Due to the relatively low number density of the quasar sample, the bump in the power spectrum due to the baryon density, Ω_b, is not clearly visible. The effect of the baryon density is, however, to distort the overall shape of the 2PCF. The degree of distortion makes it an interesting alternate measure of the baryonic signature. Assuming a scale-independent linear bias and a spatially flat universe, we combined the observed quasar 2PCF and the predicted matter 2PCF to put constraints on Ω_b and Ω_Λ (the cosmological constant). Our result was fitted as 0.80 -2.8Ω_b < Ω _Λ < 0.90 - 1.4Ω_b at the 2σ confidence level. The "mean" bias parameter of our quasar sample is 1.59 σ₈^-1 (for Ω_b = 0.04 and Ω_Λ = 0.7), where σ₈ is the top-hat mass fluctuation amplitude at 8 h^-1 Mpc. We also estimated the corresponding bias parameter of quasars at z = 0, b_QSO.Fry(0), assuming Fry's bias evolution model. For Ω_b = 0.04, Ω_Λ = 0.73, and Ω_d = 0.23, we found b_QSO.Fry(0) = 0.54 + 0.83 σ₈^-1 which is valid for 0.6 < σ₈ < 1.0.