Towards a Precise Measurement of Matter Clustering: Lyman-alpha Forest Data at Redshifts 2-4
Abstract
We measure the filling factor, correlation function, and power spectrum of transmitted flux in a large sample of Lya forest spectra, comprised of 30 Keck HIRES and 23 Keck LRIS spectra. We infer the linear matter power spectrum P(k) from the flux power spectrum P_F(k), using an improved version of the method of Croft et al. (1998) that accounts for the influence of redshift-space distortions, non-linearity, and thermal broadening on the shape of P_F(k). The evolution of P(k) over the redshift of the sample (z ~ 2-4) is consistent with gravitational instability, implying that non-gravitational fluctuations do not make a large contribution. Our fiducial measurement of P(k) is from data with 2.3<z<2.9 ( = 2.72). The P(k) has amplitude Delta^2(k_p)= 0.54^+0.14_-0.12 at k_p=0.03(kms^-1)^-1; it is well described by a power-law of index nu = -2.47 +/-0.06 or by a CDM-like form with shape Gamma'= 9.6^+4.3_-4.8*10^-4 (kms^-1)^-1 at z=2.72 (1 sig errors). This is close to the predictions of leading cosmological models, but different enough to create slight tensions on parameters when combined with other constraints. For Omega_m=0.4, Omega_Lam=0.6, and inflationary index n=1, the shape Gamma at z=0 = 0.12^+0.05_-0.06 (h^-1mpc)^-1. Matching the observed cluster mass function in flat models requires Omega_m= 0.50^+0.13_-0.10 for Gamma=0.15, and higher Omega_m for larger Gamma. A COBE-normalized model with Omega_m=0.4, Omega_Lam=0.6, h=0.65, Omega_b h^2=0.02 requires n=0.91+/-0.03 for a tensor normalization T/S=7(1-n). A better determination of the mean opacity of the Lya forest would increase the precision of our P(k) measurement and remove the main source of systematic uncertainty.(Abridged)Keywords
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