The Lyman α forest and WMAP year three

A combined analysis of cosmic microwave background (CMB) and Lyman alpha 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 a forest data. The amplitude of the matter power spectrum sigma(8) and the spectral index n(s) inferred from the joint analysis of high-and low-resolution Lyman alpha forest data as analysed by Viel & Haehnelt are consistent with the new WMAP results to within 1 sigma. The joint analysis with the mainly low-resolution data as analysed by McDonald et al. suggests a value of sigma(8) that is similar to 2 sigma higher than that inferred from the WMAP three-year data alone. The joint analysis of the three-year WMAP and the Lyman alpha 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 alpha forest data are (sigma(8), n(s)) = (0.78 +/- 0.03, 0.96 +/- 0.01).