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 transmitted flux in a large sample of Lyα 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 redshift-space distortions, non-linearity, and thermal broadening on the shape of P F (k). The evolution of the shape and amplitude of P (k) over the redshift range of the sample (z ≈ 2−4) is consistent with the predictions of gravitational instability, implying that non-gravitational fluctuations do not make a large contribution to structure in the Lyα forest. Our fiducial measurement of P (k) comes from a subset of the data with 2.3 < z < 2.9, mean absorption redshift z = 2.72, and total path length ∆z ≈ 25. It has a dimensionless amplitude ∆ 2 (k p ) = 0.74 +0.20 −0.16 at wavenumber k p = 0.03(km s −1 ) −1 and is well described by a power-law of index ν = −2.43±0.06 or by a CDM-like power spectrum with shape parameter Γ ′ = 1.3 +0.7 −0.5 ×10 −3 (km s −1 ) −1 at z = 2.72 (all error bars 1σ). The correspondence to present day P (k) parameters depends on the adopted cosmology. For Ω m = 0.4, Ω Λ = 0.6, the best-fit shape parameter is Γ = 0.16h Mpc −1 , in good agreement with measurements from the 2dF Galaxy Redshift Survey, and the best-fit normalization is σ 8 = 0.82(Γ/0.15) −0.44 . Matching the observed cluster mass function and our measured ∆ 2 (k p ) in spatially flat cosmological models requires Ω m = 0.38 +0.10 −0.08 + 2.2(Γ − 0.15). Matching ∆ 2 (k p ) in COBEnormalized, flat CDM models with no tensor fluctuations requires Ω m = (0.29 ± 0.04)n −2.89 h −1.9 65 , and models that satisfy this constraint are also consistent with our measured logarithmic slope. The Lyα forest complements other observational probes of the linear matter power spectrum 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 a cosmological model based on inflation, cold dark matter, and vacuum energy.

Simulations of Damped Lyα and Lyman Limit Absorbers in Different Cosmologies: Implications for Structure Formation at High Redshift

“…A model with somewhat less small-scale power, such as the lower amplitude LCDM model favored by recent Lya forest studies (McDonald et al 2000 ;Croft et al 2001), might fare better in this regard, perhaps matching the observed DLA abundance with a closer to the v c,min expected photoionization value. We are unable to make predictions for total absorption in the TCDM model with our current simulations because the paucity of structure above our resolution threshold makes our extrapolation procedure unreliable.…”

Early Quintessence in Light of the Wilkinson Microwave Anisotropy Probe

“…n s In Figure 2, we compare the prediction of our models for the matter power spectrum with data extracted from galaxy catalogs (e.g., Two-Degree Field Galaxy Redshift Survey [2dFGRS]; Percival et al 2001;Verde et al 2002;Peacock et al 2001) or the Lya forest (Gnedin & Hamilton 2002;Croft et al 2002). In view of the uncertainties from bias and nonlinearities, the agreement is good for all models (A-D).…”

“…The 2dFGRS (Percival et al 2001;Peacock et al 2001;Verde et al 2002) and Lya (Gnedin & Hamilton 2002;Croft et al 2002) data have been evolved to , although we have not convolved our theoretical data with z p 0 the experimental window functions. The galaxy power spectrum has a bias compared to theoretical predictions that is not included in the figure. energy T into potential energy V, effectively "stopping" the field.…”

Observational probes of cosmic acceleration

“…However, even after marginalizing over these parameters there is enough information in the clustering statistics of the flux F to constrain the shape and amplitude of the matter power spectrum (e.g., Croft et al 2002;McDonald et al 2006). Lyα forest surveys conducted for BAO allow high precision measurements of flux correlations on smaller scales, so they have the statistical power to achieve tight constraints on matter clustering.…”