Light Propagation in Inhomogeneous Universes. IV. Strong Lensing and Environmental Effects

We study the gravitational lensing of high-redshift sources in a LCDMuniverse. We have performed a series of ray-tracing experiments, and selected asubsample of cases of strong lensing (multiple images, arcs, and Einsteinrings). For each case, we identify a massive galaxy that is primarilyresponsible for lensing, and studied how the various density inhomogeneitiesalong the line of sight (other galaxies, background matter) affect theproperties of the image. The matter located near the lensing galaxy, andphysically associated with it, has a small effect. The background matterincreases the magnification by a few percents at most, while nearby galaxiescan increase it by up to about 10 percent. The effect on the image separationis even smaller. The only significant effect results from the random alignmentof physically unassociated galaxies, which can increase the magnification byfactors of several, create additional images, and turn arcs into rings. Weconclude that the effect of environment on strong lensing in negligible ingeneral, and might be important only in rare cases. We show that our conclusiondoes not depend on the radial density profile of the galaxies responsible forlensing.Comment: 23 pages, 7 figures (one in color). Accepted for publication in The Astrophysical Journal. Minor typos correcte