Intrinsic and extrinsic gravitational flexions

ABSTRACT The topic of this paper is a generalization the linear model for intrinsic alignments galaxies to flexions: In model, third moments brightness distribution reflect distortions elliptical caused by derivatives gravitational potential, or, equivalently, gradients tidal fields. With extension mediating between and fields with quantification shape galaxy at order provided HOLICs-formalism, we are able compute angular spectra flexions cross-spectra weak lensing flexions. Spectra typically an magnitude smaller than flexions, exactly as in case ellipticity comparison shear. We find negative cross-correlation extrinsic too, complementing analogous correlation ellipticity. After discussing physical details alignment provide their scaling properties, quantify observability estimate Fisher-formalism how well parameter can be determined from Euclid-like survey. Intrinsic very difficult measure yield appreciable signals only highly optimistic choices noise levels, while being basically undetectable more realistic flexion measurement errors.