Marcos Lima

Gravitational Lensing

Gravitational lensing is the distortion of photons from distant galaxies due to the gravitational field of the intervening large-scale structure in the Universe.

In the weak lensing regime, the gravitational potentials of field galaxies produce very small distortions which, when accounted for in a large statistical sample, have a lot of cosmological information, probing the expansion history as well as the growth of structure.

In the strong lensing regime, gravity produced by galaxy clusters induce large distortions in the images of distant galaxies, which can be used to study the density profiles of clusters.

Because lensing is merely a deflection of light rays (no creation/disappearance of photons), it preserves surface brightness (flux per solid angle). As a result, since the sizes of galaxies become larger in the direction of deep potentials, their fluxes also increase by the same factor. This factor is the lensing magnification, which captures both isotropic (convergence) and anisotropic (shear) distortions in galaxy shape, and has interesting effects in the properties of the distant source galaxies, such as their number density. Even without lensing, these faraway galaxies can contaminate observations of unresolved objects at intermediate redshifts such as galaxy clusters. Lensing magnification further increases this contamination.

With Bhuvnesh Jain, Mark Devlin and James Aguirre, I worked on the effect of lensing on the population of submillimeter galaxies at high redshifts and also on the effect that this population can have on unresolved galaxy clusters detected through their Sunyaev Zel'dovich effect.