MIT Kavli Institute Directory

I study weak gravitational lensing in galaxy clusters. Mass bends the path of light traveling near it. So the mass within a galaxy cluster will alter the path of light from a galaxy sitting behind the cluster as that light travels from itself to telescopes here on Earth. Because the cluster deflects light in a way completely analogous to a traditional glass lens, we call it a gravitational lens. The first order effect of the lens is to deflect the apparent image of the background galaxies from their true locations in space. The second order effect of the lens is to brighten and elongate the images of the background galaxies. The third order effect of the lens is to bend and render lopsided the apparent images of the background galaxies. The combination of these distortions reveals the underlying mass structure of the gravitational lens. As the primary component of the lens is dark matter, gravitational lensing is one of very few ways to empirically probe dark matter's structure. The third order lensing effect, which I study, has the potential to reveal higher order substructure within the cluster, such as galaxy halo properties.

I additionally study telescope aberrations and the effects of misalignments on telescope images. Interestingly, the distortions caused by optical lenses have an identical form mathematically those caused by gravitational lenses. Astigmatism is shear; coma is F-flexion; trefoil is G-Flexion. Fortunately these optical aberrations have different field dependences than the gravitational aberrations.