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