The effect of clustering on the equivalent width distribution of QSO Lyman-alpha clouds

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Abstract
We report a significant discrepancy between the observed equivalent width distribution p( W ) of Lyman α absorption features in intermediate-resolution QSO spectra and that expected from high-resolution spectra. It is found that, if clouds are randomly distributed, line blending cannot account for this effect, and the difference is interpreted as due to enhanced line blending caused by cloud–cloud clustering. Using a clustering model for the Lyman α clouds, it is shown how the apparent p( W ) depends on clustering properties, and an estimate of the clustering model parameters is derived by comparing the simulated p( W ) to that of the real data. The clustering model deduced in this way is derived independently of and is in excellent agreement with the observed two-point correlation function.

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