Reconstruction of small-scale galaxy cluster substructure with lensing flexion

Abstract

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 ∼25-40 per cent. When flexion is included, subhaloes down to a mass of ∼3 × 10¹² M_⊙ 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 ∼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.