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arXiv · 2611.07824

GradFlex: a Gradient-Based Method for Weak Lensing Flexion Measurement

Jiarui Sun·Jun Zhang·Toshifumi Futamase
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Abstract

Flexion, the second-order gravitational lensing distortion, probes small-scale mass distribution and complement the cosmic shear measurement. However, its detection is highly challenging due to the faint signal and the contamination arising from the intrinsic galaxy morphology. In this Letter, we present GradFlex, a new method that extracts flexion from the gradient field of galaxy surface brightness distributions without assuming a specific point-spread function model or galaxy morphology. Using surface-brightness conservation, we relate the pre- and post-lensing gradient fields and derive flexion estimators from ensemble-averaged statistics of the corresponding spins. Tests on numerical simulations across diverse galaxy morphologies and multiple noise realizations demonstrate its reliability under realistic observing conditions. Combined with shear measurements, it could tighten constraints on cluster density profiles and enable more detailed studies of substructure than shear alone.

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Jiarui Sun, Jun Zhang, Toshifumi Futamase. 2026-11-05. GradFlex: a Gradient-Based Method for Weak Lensing Flexion Measurement. https://arxiv.org/abs/2611.07824

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