Measuring dark matter substructure with galaxy-galaxy flexion statistics

It is of great interest to measure the properties of substructures in dark matter haloes at galactic and cluster scales. Here we suggest a method to constrain substructure properties using the variance of weak gravitational flexion in a galaxy-galaxy lensing context; this is a statistical method, requiring many foreground-background pairs of galaxies. We show the effectiveness of flexion variance in measuring substructures in N-body simulations of dark matter haloes, and present the expected galaxy-galaxy lensing signals. We show the insensitivity of the method to the overall galaxy halo mass, and predict the method's signal-to-noise ratio for a space-based all-sky survey, showing that the presence of substructure down to 10(9)M(circle dot) haloes can be reliably detected.