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We present a simulation analysis of weak gravitational lensing flexion andshear measurement using shapelet decomposition, and identify differencesbetween flexion and shear measurement noise in deep survey data. Taking modelsof galaxies from the Hubble Space Telescope Ultra Deep Field (HUDF) andapplying a correction for the HUDF point spread function we generate lensedsimulations of deep, optical imaging data from Hubble's Advanced Camera forSurveys (ACS), with realistic galaxy morphologies. We find that flexion andshear estimates differ in our measurement pipeline: whereas intrinsic galaxyshape is typically the dominant contribution to noise in shear estimates, pixelnoise due to finite photon counts and detector read noise is a majorcontributor to uncertainty in flexion estimates, across a broad range of galaxysignal-to-noise. This pixel noise also increases more rapidly as galaxysignal-to-noise decreases than is found for shear estimates. We provide simplepower law fitting functions for this behaviour, for both flexion and shear,allowing the effect to be properly accounted for in future forecasts forflexion measurement. Using the simulations we also quantify the systematicbiases of our shapelet flexion and shear measurement pipeline for deep Hubbledata sets such as Galaxy Evolution from Morphology and SEDs, Space TelescopeA901/902 Galaxy Evolution Survey or the Cosmic Evolution Survey. Flexionmeasurement biases are found to be significant but consistent with previousstudies.

Flexion measurement in simulations of Hubble Space Telescope data