Gravitational lensing by large-scale structures

Abstract

Decisive conclusions can not be drawn yet, but it appears as if gravitational lensing could indeed account for QSO-galaxy associations on arc-minute scales. These correlations are due to the lensing action of the dark matter inhomogeneities. Implicitly, we assume that galaxies trace the dark matter distribution, which results in a strong correlation between the dark matter density peaks and enhanced number counts of galaxies. Furthermore, we argue that galaxy lenses perturb or even destroy the effect, because galaxies are capable of producing high magnifications over a wide range of redshifts and not only in a very narrow redshift interval, as is the case with dark matter inhomogeneities. This means that galaxy lenses are very weakly or not at all correlated with the number density peaks in the galaxy counts and thus do not cause enhanced galaxy counts in the vicinity of lensed QSOs.