Absorption spectra of Q 0000 - 263 and 1442 + 101

We present a new analysis of the Ly α forest for the high-redshift QSOs 1442 + 101 (z = 3.544) and 0000 – 263 (z = 4.111). We have performed detailed profile fitting to spectra of moderate resolution and high signal-to-noise ratio. The results are compared to a more conventionally derived line list. As a result, we provide a high-redshift extension to the previously reported Ly α forest samples of Bajtlik, Duncan & Ostriker, Lu, Wolfe & Turnshek and Rauch et al. If the evolution of the number of lines per unit redshift has the functional form (1 + z)^γ then we find a best-fitting value of γ = 2.59 ± 0.49 for an equivalent width completeness limit of $${W}_\text {thr} = 0.21$$ Å. If the equivalent widths are distributed as exp( – W/W^⋆), we determine a characteristic equivalent width $${W}^{\ast} = 0.084 \pm 0.008$$ for the new data. Relating this to a column density distribution of the form $$p(N_{\text H_1}) \propto N_{\text H_1}^{-\beta}$$, we find that β ≈ 1.9. The new data combined with the Rauch et al. sample give $ ${W}^{\ast} = 0.179 \pm 0.010,$$ which corresponds to β ≈ 1.7. Our values for W^⋆ and β imply that the new data are not consistent with the typical intermediate-resolution sample. The larger values that we have determined for β are, however, consistent with high-resolution spectra.