The Lyman alpha forest towards B2 1225 + 317

We present observations of the Lyman alpha (Ly α) forest towards B2 1225 + 317 taken at a resolution of 18 km s^-1. A clean sample of Ly α forest lines is extracted after a careful profile-fitting analysis and the removal of the absorption lines of heavy elements. The sample is analysed for statistical properties. Eighty per cent of the column densities are < 10¹⁴ cm^-2. A single power law is inconsistent with the column density distribution and a steepening/break in the distribution is indicated. The average velocity dispersion parameter is 29.4 km s^-1. We find 3σ evidence for a correlation between column density and the velocity dispersion parameter. The correlation, however, is mainly the result of narrow lines and weakens to 1.2σ if lines with a velocity dispersion parameter smaller than 20 km s^-1 are excluded. An excess of line pairs with velocity separation ≤ 100 km s^-1 over the expected number is found.