Gravitational-Mass Imaging of CDM Substructure

I propose the novel method of “gravitational-mass imaging” to detect and quantify luminous and dark-matter substructure in gravitational-lens galaxies. The method utilizes highly-magnified Einstein rings and arcs as sensitive probes of small perturbations in the lens potential (due to the presence of mass substructure), reconstructing the gravitational lens potential non-parametrically. Simulations show that the implemented algorithm can image the smooth mass distribution of a typical lens galaxy with ME=10 11 M⊙ – exhibiting reasonable signal-to-noise Einstein rings – as well as compact substructure with masses as low as ME∼10 8 M⊙, if present. Gravitationalmass imaging of dark-matter substructure around massive galaxies can provide a new window on the standard cold-dark-matter paradigm, using very different physics than ground-based direct-detection experiments, and simultaneously probe the hierarchical structure-formation model.