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 M_E=10^{11} Msun - exhibiting reasonable signal-to-noise Einstein rings - as well as compact substructure with masses as low as M_E~10^8 Msun, if present. Gravitational-mass 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