THE LYMAN-ALPHA FOREST OF PKS 2126-158 AT HIGH-RESOLUTION

The spectrum of the quasar PKS 2126-158 (z(em) = 3.27) has been observed at the resolution of 14 km s in the wavelength interval 4750-7000 angstrom. We give a list of Lyalpha absorption lines and metal-line systems. Column densities N and Doppler widths b are derived by a fitting procedure. Velocity structures up to 300 km s-1 are found in the strongest C iv doublets. Although selection effects could explain the observed b-N(HI) correlation for the Lyalpha lines, an intrinsic deficit of strong lines with low b values is present in our spectrum. The present data have been merged with other high-resolution data available in the literature to determine the overall column density distribution. A simple power-law fit N(HI)-beta gives beta = 1.7; however, a better description of the data is obtained with a flatter power law with beta = 1.5 and a break at log N(H I) approximately 15, a feature predicted by some theoretical Lyalpha cloud models. A new analysis of the proximity effect gives a UV background flux 7 x 10(-22) ergs s-1 cm-2 Hz-1 sr-1, not far from the integrated quasar contribution.