Reconstruction of small-scale galaxy cluster substructure with lensing flexion

We present a 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 $\sim25-40\%$. When flexion is included, subhaloes down to a mass of $\sim3\times10^{12}$ M$_\odot$ 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 $\sim13\%$, 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.