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

Abstract

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 is reported. It is found that, if clouds are randomly distributed, line blending cannot account for this effect. 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