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 spectra 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 z-space distortions, non- linearity, and thermal broadening on P_F(k). The evolution of the shape and amplitude of P(k) over the range 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) comes from data with <z> = 2.72. It has amplitude Delta^2(k_p)=0.74^0.20_-0.16 at wavenumber k_p=0.03 (km/s)^-1 and is well described by a power-law of index -2.43 +/- 0.06 or by a CDM-like power spectrum with shape parameter Gamma'=1.3^+0.7_-0.5*10^-3 (km/s) at z=2.72. For Omega_m=0.4, Omega_Lam=0.6, the best-fit Gamma =0.16 (h^-1mpc)^-1, in good agreement with the 2dF Galaxy Redshift Survey, and the best-fit sigma_8=0.82 (Gamma/0.15)^-0.44. Matching the observed cluster mass function and our Delta^2(k_p) in spatially flat models requires Omega_m=0.38^+0.10_-0.08 + 2.2 (Gamma-0.15). Matching Delta^2(k_p) in COBE-normalized, flat CDM models with no tensor fluctuations requires Omega_m = (0.29 +/-0.04) n^-2.89 h_65^-1.9. The Lya forest complements other probes of P(k) by constraining a regime of redshift and lengthscale not accessible by other means, and the consistency of these inferred parameters with independent estimates provides further support for inflation, cold dark matter, and vacuum energy (abridged).
Highlights
We measure the filling factor, correlation function, and power spectrum of transmitted flux in a large sample of Lyα forest spectra, comprised of 30 Keck HIRES spectra and 23 Keck Low Resolution Imaging Spectrometer (LRIS) spectra
The theoretical model that motivates our method for the second step is the “Fluctuating Gunn-Peterson Approximation” (FGPA; see Rauch et al 1997; CWKH; Weinberg et al 1998b), which describes the relation between Lyα opacity and matter density for the diffuse intergalactic gas that produces most of the Lyα forest absorption at high redshift
The parameters T0 and α depend on the reionization history and on the spectral shape of the UV background; they can be predicted theoretically with the formalism of Hui & Gnedin (1997) and constrained observationally with techniques described by Schaye et al (1999, 2000), Bryan & Machacek (2000), Ricotti et al (2000), and McDonald et al (2000b)
Summary
Over the last few years, the study of the Lyα forest has been revolutionized by high-resolution spectra (mostly using the HIRES spectrograph [Vogt et al 1994] on the Keck telescope), by measurements of coherent absorption along lines of sight to quasar pairs (Bechtold et al 1994; Dinshaw et al 1994; Crotts & Fang 1998), and by a new. Donald & Miralda-Escude 1999; Feng & Fang 2000; Hui et al 2000), and the geometry of the universe (Hui 1999; McDonald & Miralda-Escude 1999). Observational Lyα forest data have been used to constrain these quantities by Croft et al (1999b, hereafter CWPHK), McDonald et al (2000, hereafter M00), and Nusser & Haehnelt (2000). In this paper we present flux statistics measured from two
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