On the Shape of Dark Matter Halos in the Galaxy Cluster Abell 3827 and the Scattering Cross-Section of Dark Matter

Four bright elliptical galaxies lie within the central 20 kpc of the galaxy cluster Abell 3827, indicative of an ongoing merger. Gravitational lensing has already been used to measure the offsets between dark and luminous matter. Existing measurements of an offset in one of the galaxies in this cluster suggests the presence of self-interacting dark matter (SIDM). The self-interactions scatter the dark matter (DM) particles, separating the DM halo from the collisionless stellar mass. However, offsets are not the only prediction of SIDM. Numerical simulations of some models of SIDM predict colliding halos will develop a skew in the shape of a tail. For this thesis I have developed two new parametric models to detect these tails, using gravitational lensing. These are then implemented to reconstruct the mass distribution in Abell 3827, using existing HST data, together with new integrated field spectroscopy observations from VLT/MUSE. There are three main findings. Firstly, in the new mass model of Abell 3827 there are now two galaxies where dark to luminous matter offsets are present. These offsets suggest an effective cross section for DM of . Secondly, the shape of the DM halo does not significantly alter the predicted offsets between the peak of the dark and luminous matter, compared to a model without skew. Finally, there are tentative signs that there may be a tail of scattered DM particles trailing one of the offset galaxies in Abell 3827.