The Lyman α forest and WMAP year three

Abstract

A combined analysis of cosmic microwave background (CMB) and Lyman α forest data can constrain the matter power spectrum from small scales of about 1 h-1 Mpc all the way to the horizon scale. The long lever arm and complementarity provided by such an analysis have previously led to a significant tightening of the constraints on the shape and the amplitude of the power spectrum of primordial density fluctuations. We present here a combined analysis of the WMAP three-year results with Lyman α forest data. The amplitude of the matter power spectrum σ 8 and the spectral index ns inferred from the joint analysis of high- and low-resolution Lyman α forest data as analysed by Viel & Haehnelt are consistent with the new WMAP results to within 1σ. The joint analysis with the mainly low-resolution data as analysed by McDonald et al. suggests a value of σ 8 that is ~2σ higher than that inferred from the WMAP three-year data alone. The joint analysis of the three-year WMAP and the Lyman α forest data also does not favour a running of the spectral index. The best-fitting values for a combined analysis of the three-year WMAP data, other CMB data, 2-degree Field (2dF) data and the Lyman α forest data are (σ 8,ns) = (0.78 ± 0.03,0.96 ± 0.01). © 2006 The Authors. Journal compilation © 2006 RAS.