Perturbative reconstruction of a gravitational lens: when mass does not follow light

摘要

Aims. The structure and potential of a complex gravitationallens is reconstructed using the perturbative method presented in Alard(2007, MNRAS, 382, L58; 2008, MNRAS, 388, 375). This lens is composedof 6 galaxies belonging to a small group. Methods. The lens inversion is reduced to the problem ofreconstructing non-degenerate quantities: the 2fields of theperturbative theory of strong gravitational lenses. Since in theperturbative theory the circular source solution is analytical, thegeneral properties of the perturbative solution can be inferreddirectly from the data. As a consequence, the reconstruction of theperturbative fields is not affected by degeneracy, and finding the bestsolution is only a matter of numerical refinement. Results. The local shape of the potential and density of thelens are inferred from the perturbative solution, revealing theexistence of an independent dark component that does not follow light. Conclusions. The most likely explanation is that the particularshape of the dark halo is due to the merging of cold dark matter halos.This is a new result illustrating the structure of dark halos on thescale of galaxies. Key words: gravitational lensing - dark matter