A Model-Independent Characterisation of Strong Gravitational Lensing by Observables

Jenny Wagner

doi:10.3390/universe5070177

Abstract

When light from a distant source object, like a galaxy or a supernova, travels towards us, it is deflected by massive objects that lie in its path. When the mass density of the deflecting object exceeds a certain threshold, multiple, highly distorted images of the source are observed. This strong gravitational lensing effect has so far been treated as a model-fitting problem. Using the observed multiple images as constraints yields a self-consistent model of the deflecting mass density and the source object. As several models meet the constraints equally well, we develop a lens characterisation that separates data-based information from model assumptions. The observed multiple images allow us to determine local properties of the deflecting mass distribution on any mass scale from one simple set of equations. Their solution is unique and free of model-dependent degeneracies. The reconstruction of source objects can be performed completely model-independently, enabling us to study galaxy evolution without a lens-model bias. Our approach reduces the lens and source description to its data-based evidence that all models agree upon, simplifies an automated treatment of large datasets, and allows for an extrapolation to a global description resembling model-based descriptions.

Highlights

Forty years ago, in 1979, two images of the quasar QSO 0957+561 were observed, [1], which marked the discovery of strong gravitational lenses
In [23], we developed this idea further by assuming a constant A( x) in the area spanned by the quadrupole of an unresolved multiple image or in the area spanned by the convex hull of all identifiable reference points of a resolved multiple image
We showed that the larger the area of each multiple image from which the observables are extracted, the smaller the confidence bounds on the inferred local lens properties

Summary

Introduction

In 1979, two images of the quasar QSO 0957+561 were observed, [1], which marked the discovery of strong gravitational lenses. Observations of multiple images have been routinely used to probe the deflecting mass-density distribution, in particular in order to infer its dark matter content and dark matter properties—see, e.g., [7,8] for galaxy-scale lens surveys, or [9,10] for galaxy-cluster-scale lens surveys. Attempts to infer the cosmic spatial curvature, the cosmic matter density parameter, and dark energy properties of the current cosmological concordance model and its potential extensions are being pursued with galaxy-scale and cluster-scale lenses, [16,17,18]. Even after forty years of strong gravitational lensing studies, it still is a subject of high research interest because unprecedented observations, like supernova (SN) Refsdal, [19], or the recently discovered fast radio

Methods

Results

Conclusion