Seminar by Jenny Wagner (University of Helsinki)

Abstract

Strong gravitational lensing has emerged as a standard method for mapping the mass densities of cosmic structures or for inferring parameters of the cosmological concordance model, such as the Hubble constant. In this talk, I will introduce those properties of a light-deflecting cosmic structure that can be uniquely and directly determined from observables without any lens model assumptions. These properties constitute the maximum information common to all model-based mass maps and require less than a second of computing time. The derivation of these characteristics also reveals the most general class of lensing degeneracies and a simple physical interpretation of their origins. I will showcase the power of this approach in two galaxy clusters: we can infer a least-model-dependent smoothness scale for dark matter,
reconstruct the morphology of the lensed source galaxy, and even infer global properties
of the lensing cluster in combination with complementary data. Thus, with an increasing
amount of data, this approach will allow us to gain a deeper understanding of the
necessary amount and properties of dark matter in cosmic structures.