# Hubble Frontier Fields: systematic errors in strong lensing models of galaxy clusters - Implications for cosmography

## TL;DR

This paper investigates systematic errors in strong lensing models of galaxy clusters using simulated data, highlighting their impact on cosmological parameter estimation and emphasizing the importance of wide-field imaging and redshift accuracy.

## Contribution

It provides a detailed analysis of systematic errors in parametric strong lensing models and their effects on cosmological constraints, using simulated Hubble Frontier Fields-like clusters.

## Key findings

- Substructures affect multiple image positions and tighten cosmological constraints.
- Wide-field imaging reduces systematic errors in lensing models.
- Photometric redshifts improve cosmological parameter estimates.

## Abstract

Strong gravitational lensing by galaxy clusters is a fundamental tool to study dark matter and constrain the geometry of the Universe. Recently, the Hubble Space Telescope Frontier Fields programme has allowed a significant improvement of mass and magnification measurements but lensing models still have a residual root mean square between 0.2 arcsec and few arcsec- onds, not yet completely understood. Systematic errors have to be better understood and treated in order to use strong lensing clusters as reliable cosmological probes. We have analysed two simulated Hubble-Frontier-Fields-like clusters from the Hubble Frontier Fields Comparison Challenge, Ares and Hera. We use several estimators (relative bias on magnification, den- sity profiles, ellipticity and orientation) to quantify the goodness of our reconstructions by comparing our multiple models, optimized with the parametric software LENSTOOL , with the input models. We have quantified the impact of systematic errors arising, first, from the choice of different density profiles and configurations and, secondly, from the availability of con- straints (spectroscopic or photometric redshifts, redshift ranges of the background sources) in the parametric modelling of strong lensing galaxy clusters and therefore on the retrieval of cosmological parameters. We find that substructures in the outskirts have a significant im- pact on the position of the multiple images, yielding tighter cosmological contours. The need for wide-field imaging around massive clusters is thus reinforced. We show that competitive cosmological constraints can be obtained also with complex multimodal clusters and that photometric redshifts improve the constraints on cosmological parameters when considering a narrow range of (spectroscopic) redshifts for the sources.