Gravitational flexion, its measurement and its application to galaxy clusters
Final Report Abstract
In conclusion, we tested the performance of a newly-developed method for shape measurements, investigating in particular its ability to recover distortions induced by gravitational flexion. This algorithm, which exploits principal-component analysis to de-noise the images, has proven to be very versatile and easily applicable to new sets of data, since it does not require any prior knowledge on the properties of the objects whose shapes are going to be measured. Nonetheless, under the observational conditions of typical weak-lensing survey data nowadays available, not even this algorithm is able to provide a reliable estimate of distortions caused by gravitational flexion. A deeper understanding of the role played by pixel noise in the measurements of the flexion estimators is indispensable before the current techniques for shape measurements may be used to estimate flexion in real data. Only then, the potential of flexion may be extensively exploitable. These results may appear negative. Nonetheless, it appears important to have clarified that, despite the considerable hope pinned on flexion measurements e.g. for cluster substructure recovery, it is very unlikely that it will be possible in the foreseeable future to measure flexion off more than very few, sufficiently bright background-galaxy images per cluster field.
