Gravitational lensing and quasar-galaxy correlations

Webster and colleagues reported in 1988 a significant excess of foreground galaxies in the vicinity of quasars. It is shown that if the effect is due to gravitational lensing, then the quasar-galaxy correlation must be smaller than the reported level by a factor ~ 2 and/or the magnitude limit of the survey must be few tenths of a magnitude brighter than the stated limit of B_J_ = 18.7. Also, contrary to popular belief, the effect does not require that halos of foreground galaxies be composed of microlenses (stars, black holes, etc); the quasar-galaxy correlation works equally well with smooth halos. These conclusions follow directly from the quasar luminosity function and are independent of the structure of the lens.