Gravitational lensing by clusters of galaxies offers a powerful probe of their structure and mass distribution. Several research groups have developed techniques independently to achieve this goal. While these methods have all provided remarkably high-precision mass maps, particularly with exquisite imaging data from the Hubble Space Telescope (HST), the reconstructions themselves have never been directly compared. In this paper, we present for the first time a detailed comparison of methodologies for fidelity, accuracy and precision. For this collaborative exercise, the lens modelling community was provided simulated cluster images that mimic the depth and resolution of the ongoing HST Frontier Fields. The results of the submitted reconstructions with the un-blinded true mass profile of these two clusters are presented here. Parametric, free-form and hybrid techniques have been deployed by the participating groups and we detail the strengths and trade-offs in accuracy and systematics that arise for each methodology. We note in conclusion that several properties of the lensing clusters are recovered equally well by most of the lensing techniques compared in this study. For example, the reconstruction of azimuthally averaged density and mass profiles by both parametric and freeform methods matches the input models at the level of ~10 per cent. Parametric techniques are generally better at recovering the 2D maps of the convergence and of the magnification. For the best-performing algorithms, the accuracy in the magnification estimate is ~10 per cent at μtrue = 3 and it degrades to ~30 per cent at μtrue ~ 10.
Bibliographical noteFunding Information:
We thank T. Treu for the helpful discussion. MM acknowledges support from the Italian Ministry of Foreign Affairs and International Cooperation, Directorate General for Country Promotion, from INAF via PRIN-INAF 2014 C.R.A. 1.05.01.94.02, and from ASI via contract ASI/INAF/I/023/12/0. This work was supported in part by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan and JSPS KAKENHI GrantNumber 26800093 and 15H05892. AZ is supported by NASA through Hubble Fellowship grant #HST-HF2-51334.001-A awarded by STScI, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. JMD acknowledges support of the consolider project CSD2010-00064 and AYA2012-39475-C02-01 funded by the Ministerio de Economia y Competitividad, Spain. We acknowledge the lens modelling community for enthusiastically participating in this collaborative project to compare and contrast mass models. Finally, we want to thank the anonymous referees for their comments and suggestions that helped to improve the quality of the manuscript significantly.
- Galaxies: clusters: general
- Galaxies: high-redshift
- Gravitational lensing: strong
- Gravitational lensing: weak