The implications of lenses for galaxy structure

Abstract

The 12 possible cases of lensing by isolated galaxies are inverted using a set of five simple models. The set incorporates five lenses with four images, four with two images, and three radio rings. The image positions for all of the point image lenses are satisfied to within observational errors by any of five simple models. The four image lenses and the rings tightly constrain the mass inside the ring of images, and, to a lesser extent, the ellipticities, orientations, and positions. The radial structure of the lens quadrupole moment is affected the most; models with the same quadrupole tend to require the same ellipticities, orientations, and positions even after drastic changes in the structure of the monopole. The range and variability of the solutions which generate a particular configuration are stated as the key issues in using lenses as tools for exploring the structure of galaxies and the universe.