How much dark matter really matters?

TL;DR

This paper examines how standard mass models in strong gravitational lensing may overestimate dark matter content, emphasizing the importance of model-independent observations for accurate dark matter inference.

Contribution

It demonstrates that removing pre-defined mass models reveals direct constraints on local mass properties, challenging assumptions about dark matter amounts in lensing.

Findings

Standard models overestimate dark matter in lensing masses.

Model-independent observations provide direct constraints on local mass properties.

Reconstruction methods influence inferred dark matter content.

Abstract

Strong gravitational lensing is a key probe to trace dark matter. It assumes that mass curves spacetime so that light from a background source is deflected on its way to the observer. If dark matter contributes the major part to a massive cosmic structure, reconstructing the latter from strong-lensing observables allows us to infer characteristics of dark matter. Standard reconstructions fit a pre-defined mass-density model to the data. In this essay, I show how these mass models over-estimate the dark-matter contents of light-deflecting masses. Eliminating these models from the reconstruction reveals that observations directly constrain local properties of light-deflecting masses. How much dark matter is really needed in strong-gravitational-lensing effects and how much do we make up by our model choices?