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 observ ed at the resolution of 14 km s in the wavelength interval 4750-7000 a ngstrom. We give a list of Lyalpha absorption lines and metal-line sys tems. 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 stro ngest C iv doublets. Although selection effects could explain the obse rved b-N(HI) correlation for the Lyalpha lines, an intrinsic deficit o f strong lines with low b values is present in our spectrum. The prese nt 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 d escription 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 proxim ity effect gives a UV background flux 7 x 10(-22) ergs s-1 cm-2 Hz-1 s r-1, not far from the integrated quasar contribution.