Reconstruction of small-scale galaxy cluster substructure with lensing flexion

We present reconstructions of galaxy-cluster-scale mass distributions from simulated gravitational lensing data sets including strong lensing, weak lensing shear, and measurements of quadratic image distortions - flexion. The lensing data is constructed to make a direct comparison between mass reconstructions with and without flexion. We show that in the absence of flexion measurements, significant galaxy-group scale substructure can remain undetected in the reconstructed mass profiles, and that the resulting profiles underestimate the aperture mass in the substructure regions by similar to 25-40 per cent. When flexion is included, subhaloes down to a mass of similar to 3 x 10(12) M-circle dot can be detected at an angular resolution smaller than 10 arcsec. Aperture masses from profiles reconstructed with flexion match the input distribution values to within an error of similar to 13 per cent, including both statistical error and scatter. This demonstrates the important constraint that flexion measurements place on substructure in galaxy clusters and its utility for producing high-fidelity mass reconstructions.