Weak lensing of QSOs by the large scale structure

We detect a positive angular correlation between high redshift QSOs and foreground galaxies. The QSOs are taken from the optically selected LBQS Catalog (Hewett et al.(3)), while the galaxies are from the APM survey. The correlation amplitude is about a few percent on angular scales of over a degree. The correlations are a sensitive function of QSO apparent magnitude; they are strongest for m(Q) < 17.5 and undetectable for m(Q) < 18.5. The correlations are ascribed to the weak lensing effect of the foreground dark matter, which is traced by the APM galaxies. The amplitude of the effect found here is compared to the predictions from the literature, and to the predictions of our phenomenological model, which is based on the observed counts-in-cells distribution of APM galaxies. While the latter agree reasonably well with analytical predictions (Dolag & Bartelmann,(2) and Sanz et al.(5)), both underpredict the observed correlation amplitude on degree angular scales.