Pruning the Lyman forest of Q1331 + 170

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Abstract
We present a study of the Lyman α forest of the QSO 1331 +170 in the range 1.67 abs < 2.10 at 18 km s−1 resolution. Our analysis includes a careful search for previously unidentified heavy-element systems, and incorporates detailed deblending of Lyα forest lines from heavy-element lines. Various statistical properties of Lyα forest lines, such as distributions of equivalent widths, H I column densities, Doppler parameters and pair-velocity separations, are computed. The effect on these properties of employing different limiting approaches to heavy- eiement deblending, and profile-fitting of the lines, is illustrated. Our data suggest that the NH distribution may not be fitted adequately by a single power law, i.e., that there may be a relative deficit of strong lines as compared with the predictions of a single power law. However, larger samples are required to verify this deficit. The median b value is ≈ 32 km s−1 No significant correlation is observed between NH and b. An excess on the scale of ∼100 km s−1 is seen in the pair-velocity correlations, at the level of ∼ 2.6σ for the conservative sample and at the level of ∼ 4.9(7.for the less conservative sample. Marginal excess correlation is seen in both the samples at the ≿2σ level on scales of ∼800–1000 km s−1, and also on scales of ∼6000 km s−1.

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