Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2011-10-11
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
21 pages, 8 figures, 4 tables
Scientific paper
We use data on massive galaxy clusters (M_cluster > 8 10^14 h^(-1) M_solar within a comoving radius of R_cluster = 1.5 h^(-1)Mpc) in the redshift range 0.05 < z < 0.83 to place constraints on the dark energy equation-of-state parameters (w_0,w_a), as well as on the nonrelativistic matter density parameter Omega_m, on the amplitude of mass fluctuations sigma_8, on the index n of the power-law spectrum of the density perturbations, and on the Hubble constant H_0. We show that present data weakly constrain (w_0,w_a) around the values corresponding to a cosmological constant, i.e. (w_0,w_a) = (-1,0). Cluster data alone prefer low values of the amplitude of mass fluctuations, sigma_8 < 0.69 (1 sigma C.L.), and large amounts of nonrelativistic matter, Omega_m > 0.38 (1 sigma C.L.), in slight tension with the LambdaCDM concordance cosmological model (the results are however compatible with LambdaCDM at 2sigma). We derive a sigma_8 normalization relation, sigma_8 Omega_m^(1/3) = 0.49 \pm 0.06 (2 sigma C.L.), and we find that the fit to data is almost independent of n and only very weakly dependent on H_0. Combining cluster data with baryon acoustic oscillation observations, cosmic microwave background data, Hubble constant measurements, Hubble parameter determination from passively-evolving red galaxies, and magnitude-redshift data of type Ia supernovae, we find sigma_8 = 0.73^(+0.03)_(-0.03), Omega_m = 0.28^(+0.03)_(-0.02), w_0 = -1.14^(+0.14)_(-0.16), w_a = 0.85^(+0.42)_(-0.60), H_0 = 69.1^(+1.3)_(-1.5) km/s/Mpc (all 1 sigma C.L. errors), in substantial agreement with the concordance cosmological model. Very similar results are found in the case of time-evolving dark energy with a constant equation-of-state parameter w = const (the XCDM parametrization). Finally, we show that the impact of bounds on (w_0,w_a) is to favor top-down phantom models of evolving dark energy.
Campanelli Leonardo
Fogli Gian Luigi
Kahniashvili Tina
Marrone Antonio
Ratra Bharat
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