The matter power spectrum from the Lyα forest: an optical depth estimate
Abstract
We measure the matter power spectrum from 31 Lyα spectra spanning the redshift range of 1.63.6. The optical depth, τ, for Lyα absorption of the intergalactic medium is obtained from the flux using the inversion method of Nusser & Haehnelt. The optical depth is converted to density by using a simple powerlaw relation, τ ~ (1 + δ)^{α}. The nonlinear 1D power spectrum of the gas density is then inferred with a method that makes simultaneous use of the one and twopoint statistics of the flux and compared against theoretical models with a likelihood analysis. A cold dark matter model with standard cosmological parameters fits the data well. The powerspectrum amplitude is measured to be (assuming a flat Universe), σ_{8} = (0.92 +/ 0.09) × (Ω_{m}/0.3)^{0.3}, with α varying in the range of 1.561.8 with redshift. Enforcing the same cosmological parameters in all four redshift bins, the likelihood analysis suggests some evolution in the temperaturedensity relation and the thermal smoothing length of the gas. The inferred evolution is consistent with that expected if reionization of HeII occurred at z ~ 3.2. A joint analysis with the Wilkinson Microwave Anisotropy Probe results together with a prior on the Hubble constant as suggested by the Hubble Space Telescope key project data, yields values of Ω_{m} and σ_{8} that are consistent with the cosmological concordance model. We also perform a further inversion to obtain the linear 3D power spectrum of the matter density fluctuations.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 June 2006
 DOI:
 10.1111/j.13652966.2006.10333.x
 arXiv:
 arXiv:astroph/0509563
 Bibcode:
 2006MNRAS.369..734Z
 Keywords:

 hydrodynamics: intergalactic medium: quasars: absorption lines: cosmology: theory: largescale structure of Universe;
 hydrodynamics;
 intergalactic medium;
 quasars: absorption lines;
 cosmology: theory;
 largescale structure of Universe;
 Astrophysics
 EPrint:
 Replaced with the MNRAS accepted version. Changes include additional figure and modifed text