Using the 2 degree Field galaxy redshift survey to detect gravitationally lensed quasars

Galaxy redshift surveys can be used to detect gravitationally lensed quasar s if the spectra obtained are searched for the emission lines of quasars. P revious investigations of this possibility have used simple models to show that the 2 degree Field (2dF) redshift survey could yield several tens of n ew lenses, and that the larger Sloan Digital Sky Survey should contain an o rder of magnitude more. However the particular selection effects of the sam ples were not included in these calculations, limiting the robustness of th e predictions; thus a more detailed simulation of the 2dF survey was undert aken here. The use of an isophotal magnitude limit reduces both the depth o f the sample and the expected number of lenses, but more important is the A utomatic Plate Measuring survey's star-galaxy separation algorithm, used to generate the 2dF input catalogue. It is found that most quasar lenses are classed as merged stars, with only the few lenses with low-redshift deflect ors likely to be classified as galaxies. Explicit inclusion of these select ion effects implies that the 2dF survey should contain 10 lenses on average . The largest remaining uncertainty is the lack of knowledge of the ease wi th which any underlying quasars can be extracted from the survey spectra.