The power spectrum of the flux distribution in the Lyman   forest of a large sample of UVES QSO absorption spectra (LUQAS)

The flux power spectra of the Lyman α forest from a sample of 27 quasi-stellar objects (QSOs) taken with the high-resolution Ultraviolet Echelle Spectrograph (UVES) on the Very Large Telescope (VLT) are presented. We find a similar fluctuation amplitude at the peak of the ‘3D’ flux power spectrum at k∼ 0.03 s km−1 as the study by Croft et al. (2002), in the same redshift range. The amplitude of the flux power spectrum increases with decreasing redshift if corrected for the increase in the mean flux level as expected if the evolution of the flux power spectrum is sensitive to the gravitational growth of matter density fluctuations. This is in agreement with the findings of McDonald et al. (2000) at larger redshift. The logarithmic slope of the ‘3D’ flux power spectrum, PF(k), at large scales k < 0.03 s km−1, is 1.4 ± 0.3, i.e. 0.3 shallower than that found by Croft et al. but consistent within the errors.