Separating inner and outer contributions in gravitational lenses with the perturbative method

摘要

Context. This paper presents a reconstruction of thegravitational lens SL2S02176-0513 with the singular perturbative methodpresented in Alard (2007, MNRAS, 382, L58) and Alard (2008, MNRAS, 388,375). Aims. The ability of the perturbative method to separate theinner and outer contributions of the potential in gravitational lensesis tested using SL2S02176-0513. The gravitational field of the centralgalaxy is dominated by a nearby group of galaxies located at a distanceof a few critical radius in this lens. Methods. The perturbative functionals are re-constructed usinglocal polynomials. The polynomial interpolation is smoothed by Fourierseries, and numerically fitted to the Hubble Space Telescope data witha non linear minimization procedure. The potential inside and outsidethe critical circle is derived from the reconstruction of theperturbative fields. Results. The inner and outer potential contours are verydifferent. The inner contours are consistent with the central galaxy,while the outer contours are fully consistent with the perturbationintroduced by the group of galaxies. Conclusions. The ability of the perturbative method to separatethe inner and outer contribution is confirmed, and indicates that inthe perturbative approach the field of the central deflector can beseparated from outer perturbations. The separation of the inner andouter contribution is especially important to study the shape of darkmatter halos and for the statistical analysis of the effect of darkmatter substructures. Key words: gravitational lensing: strong - dark matter - methods: data analysis