2003ApJ...597..659Q

In this paper we study the observational signatures of the lensing signal produced by dark matter halos with embedded misaligned disks. This issue is of particular interest at present, since several of the observed multiple-lens systems have magnification ratios and image geometries that are not simultaneously well fitted by standard mass models. The presence of substructure exterior to the lens has been invoked by several authors in the context of cold dark matter (CDM) models in order to explain the anomalous magnification ratios. We emphasize that the anomalous magnification ratios may be an artifact of the simple mass models currently in use; the inclusion of a misaligned disk may be able to mimic the effect of substructure. These slight spatial offsets between the dark matter halo and the disk, which are likely to occur as a consequence of interactions or mergers, lead to complex image configurations and nonstandard magnification ratios. We investigate the effects of disk misalignment on two illustrative lenses: a spiral disk embedded within a dark matter halo, and a compact, disklike component within an early-type galaxy. The expected fraction of galaxies with a misaligned disk is estimated to be of the order of the merger fraction, since all mergers are expected to progress via a transiently misaligned phase. We find that there is a significant change in all observed lensing properties due to the added complexity of such mass profiles. In particular cases, the resulting lensing geometries are unusual, with high image multiplicities. The caustic structures–both radial and tangential–are drastically modified, and the magnification ratios differ fromexpectations from standard lens models. The additional parameters required to specify the relative alignment of multiple mass components in the primary lens introduce yet another source of uncertainty in the mass modeling of gravitational lens systems.