Model-independent characterisation and model selection of gravitational lenses
Final Report Abstract
Strong gravitational lensing (SGL) is an effective astrophysical phenomenon to probe the nature and distribution of dark matter because it deflects light from background sources into several, highly distorted, magnified images. Observations of such images thus allow to characterise the unobservable dark parts of a gravitational lens causing the light deflections. In this project, a new approach to describe SGL was developed to circumvent biases due to modelling the gravitational lens and to obtain an efficient, robust, and least degenerate lens characterisation that handles large datasets with a minimum effort of intervention. We determined the unique, local, data-based information of a lens without intertwining it with global model assumptions, which had not been achieved before, maybe because developing this approach required a high degree of interdisciplinarity. The approach also allows to reconstruct the unobservable source behind the lens in the same unbiased manner. Using data from different telescopes and wavelengths of gravitational lenses on galaxy and galaxy-cluster scale, the approach was compared to state-of-the-art model-based methods, yielding the same local lens properties as all model-based approaches. Hence, we showed that these local lens properties, being directly based on observables, are the maximum information all lens models agree upon. Lens properties beyond the data points are only obtained via model assumptions. Our approach also proved highly valuable in testing model assumptions like the hypothesis whether luminous matter traces dark matter and in quickly excluding impossible configurations of multiple image candidates. Surprisingly, these new insights into the SGL formalism inspired us to derive the mathematically sound, most general, complete characterisation of all degrees of freedom in the formalism and assigning a clear physical interpretation to them, which had been an unresolved issue for 30 years. Transferring the approach to the mathematically similar formalism of plasma lensing, first promising new ways to probe plasma structures could be obtained as well. Another unexpected result entailed by the new insights was finding an explanation why gravitational lenses are often found to be approximately self-similar in observations and simulations, which now enables us to gain a deeper understanding of cosmic structures and justify the usage of certain classes of so-far heuristically inferred lens models. None of these breakthrough spin-off ideas was deemed worth further funding by the DFG, which was another surprising outcome of several rejected follow-up grant proposals. A summary of the explanation of self-similar dark matter structures often found in gravitational lenses was included into a catalogue for an exhibition on the occasion of Kepler’s 450th birthday, an essay about this idea was also honorably mentioned in the Gravity Research Foundation Essay Competition 2020 and invited for publication in IJMPD. Several newspaper articles, including one in the university news, appeared due to the Prize for Courageous Science 2020 which was awarded to the applicant by the Ministry of Science, Research, and the Arts of Baden-Württemberg honouring the project’s huge success.
Publications
- Generalised model-independent characterisation of strong gravitational lenses IV. Formalismintrinsic degeneracies. A&A 620 (2018)
J. Wagner
(See online at https://doi.org/10.1051/0004-6361/201834218) - Model-independent and model-based local lensing properties of CL0024+1654 from multiply imaged galaxies. A&A 612 (2018)
J. Wagner, J. Liesenborgs, N. Tessore
(See online at https://doi.org/10.1051/0004-6361/201731932) - A Model-Independent Characterisation of Strong Gravitational Lensing by Observables. Universe 5(7) (2019)
J. Wagner
(See online at https://doi.org/10.3390/universe5070177) - Generalised model-independent characterisation of strong gravitational lenses V. Reconstructing the lensing distance ratio by supernovae for a general Friedmann universe. MNRAS 490(2) (2019)
J. Wagner, S. Meyer
(See online at https://doi.org/10.1093/mnras/stz2717) - Generalised model-independent characterisation of strong gravitational lenses VI. The origin of the formalism intrinsic degeneracies and their influence on H0. MNRAS 487(4) (2019)
J. Wagner
(See online at https://doi.org/10.1093/mnras/stz1587) - Multiply-imaged time-varying sources behind galaxy clusters: Comparing FRBs to QSOs, SNe, and GRBs. A&A 621 (2019)
J. Wagner, J. Liesenborgs, D. Eichler
(See online at https://doi.org/10.1051/0004-6361/201833530) - Cosmic structures from a mathematical perspective 1: dark matter halo mass density profiles. GReG 52(6) (2020)
J. Wagner
(See online at https://doi.org/10.1007/s10714-020-02715-w) - Model-independent and model-based local lensing properties of B0128+437 from resolved quasar images. A&A 635 (2020)
J. Wagner, L. L. R. Williams
(See online at https://doi.org/10.1051/0004-6361/201936628) - Hamilton’s Object - a clumpy galaxy straddling the gravitational caustic of a galaxy cluster: constraints on dark matter clumping. MN- RAS 506(2) (2021)
R. E. Griffiths, M. Rudisel, J. Wagner, T. Hamilton, P.-C. Huang, C. Villforth
(See online at https://doi.org/10.1093/mnras/stab1375) - On the double-plane plasma lensing. MNRAS 509(4) (2022)
X. Er, J. Wagner, S. Mao
(See online at https://doi.org/10.1093/mnras/stab3278)
