The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: single-probe measurements and the strong power of f (z)sigma_8(z) on constraining dark energy

We present measurements of the anisotropic galaxy clustering from the Data Release 9 (DR9) CMASS sample of the Sloan Digital Sky Survey (SDSS)-III Baryon Oscillation Spectroscopic Survey (BOSS). We analyse the broad-range shape of the monopole and quadrupole correlation functions to obtain constraints, at the effective redshift z = 0.57 of the sample, on the Hubble expansion rate H(z), the angular-diameter distance DA(z), the normalized growth rate f (z))σ8(z), the physical matter density Ωmh2, and the biased amplitude of matter fluctuation b)σ8(z). We obtain {H(0.57), DA(0.57), f (0.57))σ8(0.57), Ωmh2, bs8(0.57)} = {87.6+6.7 -6.8 kms-1 Mpc-1, 1396 ± 73 Mpc, 0.428 ± 0.066, 0.126+0.008 -0.010, 1.19 ± 0.14} and their covariance matrix as well. The parameters which are not well constrained by our galaxy clustering analysis are marginalized over with wide flat priors. Since no priors from other data sets [i.e. cosmic microwave background (CMB)] are adopted and no dark energy models are assumed, our results from BOSS CMASS galaxy clustering alone may be combined with other data sets, i.e. CMB, SNe, lensing or other galaxy clustering data to constrain the parameters of a given cosmological model. We show that the major power on constraining dark energy from the anisotropic galaxy clustering signal, as compared to the angular-averaged one (monopole), arises from including the normalized growth rate f (z)σ8(z). In the case of the cosmological model assuming a constant dark energy equation of state and a flat universe (wCDM), our single-probe CMASS constraints, combined with CMB (WMAP9+SPT), yield a value for the dark energy equation-of-state parameter of w =-0.90 ± 0.11. Therefore, it is important to include f (z)σ8(z) while investigating the nature of dark energy with current and upcoming large-scale galaxy surveys.