Toward a Precise Measurement of Matter Clustering: Lyα Forest Data at Redshifts 2–4

Abstract

We measure the filling factor, correlation function, and power spectrum of\ntransmitted flux in a large sample of Lya forest spectra, comprised of 30 Keck\nHIRES spectra and 23 Keck LRIS spectra. We infer the linear matter power\nspectrum P(k) from the flux power spectrum P_F(k), using an improved version of\nthe method of Croft et al. (1998) that accounts for the influence of z-space\ndistortions, non- linearity, and thermal broadening on P_F(k). The evolution of\nthe shape and amplitude of P(k) over the range z= 2-4 is consistent with\ngravitational instability, implying that non-gravitational fluctuations do not\nmake a large contribution. Our fiducial measurement of P(k) comes from data\nwith <z> = 2.72. It has amplitude Delta^2(k_p)=0.74^0.20_-0.16 at wavenumber\nk_p=0.03 (km/s)^-1 and is well described by a power-law of index -2.43 +/- 0.06\nor by a CDM-like power spectrum with shape parameter Gamma'=1.3^+0.7_-0.5*10^-3\n(km/s) at z=2.72. For Omega_m=0.4, Omega_Lam=0.6, the best-fit Gamma =0.16\n(h^-1mpc)^-1, in good agreement with the 2dF Galaxy Redshift Survey, and the\nbest-fit sigma_8=0.82 (Gamma/0.15)^-0.44. Matching the observed cluster mass\nfunction and our Delta^2(k_p) in spatially flat models requires\nOmega_m=0.38^+0.10_-0.08 + 2.2 (Gamma-0.15). Matching Delta^2(k_p) in\nCOBE-normalized, flat CDM models with no tensor fluctuations requires Omega_m =\n(0.29 +/-0.04) n^-2.89 h_65^-1.9. The Lya forest complements other probes of\nP(k) by constraining a regime of redshift and lengthscale not accessible by\nother means, and the consistency of these inferred parameters with independent\nestimates provides further support for inflation, cold dark matter, and vacuum\nenergy (abridged).\n