| Abstract : | Intrinsic alignments are astrophysical effects that arise due to the fact that nearby galaxies are subjected to a local tidal gravitational field that influences the process of their formation, and also their shapes and sizes. The physical alignment of galaxy shapes mimics the apparent correlations of the shapes of galaxy images created by the gravitational lensing effect. In this talk, I will be describing two directions in which we have explored these effects. First, we try to build a physical model describing shape and size correlations of galaxies due to weak gravitational lensing and due to direct tidal interaction of elliptical galaxies with gravitational fields sourced by the cosmic large-scale structure. Setting up a linear intrinsic alignment model for elliptical galaxies which parameterises the reaction of the galaxy to an external tidal shear field and is controlled by the velocity dispersion, we predict intrinsic correlations and cross-correlations with weak lensing for both shapes and sizes, juxtaposing both types of spectra with lensing. Next, we generalise the linear model for intrinsic alignments of galaxies to intrinsic flexions. In this model, third moments of the brightness distribution reflect distortions of elliptical galaxies caused by third derivatives of the gravitational potential, or, equivalently, gradients of the tidal gravitational fields. Spectra for intrinsic flexions are typically an order of magnitude smaller than lensing flexions, exactly as in the case of intrinsic ellipticity in comparison to weak shear. We find a negative cross correlation between intrinsic and extrinsic gravitational flexions, too, complementing the analogous correlation between intrinsic and extrinsic ellipticity. |
