Lensing Effects of Misaligned Disks in Dark Matter Halos

We study the observational signatures of the lensing signal produced by darkmatter halos with embedded misaligned disks. This issue is of particularinterest at the present time since most of the observed multiple lens systemshave magnification ratios and image geometries that are not well-fit bystandard mass models. The presence of substructure exterior to the lens hasbeen invoked by several authors in the context of Cold Dark Matter (CDM) modelsin order to explain the anamolous magnification ratios. We emphasize that theanomalous magnification ratios may be an artifact of the simple one-componentmass models currently in use; the inclusion of a misaligned disk may be able tomimic the effect of substructure. These slight spatial offsets between the darkmatter halo and the disk, which are likely to occur during or as a consequenceof interactions or mergers, lead to complex image configurations andnon-standard magnification ratios. We investigate two illustrative lens models:a spiral disk embedded within a dark matter halo, and a compact disk-likecomponent within an elliptical galaxy. The expected fraction of galaxies with amisaligned disk is estimated to be of the order of 10%. In such cases we findthat the resultant lensing geometries are unusual, with high imagemultiplicities. The caustic structures - both radial and tangential - aredrastically modified and the magnification ratios differ compared toexpectations from standard lens models. The additional parameters required tospecify the relative alignment of the mass components in the primary lensintroduce yet another source of uncertainty in the mass modeling ofgravitational lens systems.Comment: Submitted to ApJ. 25 pages, 11 figure