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arXiv2021

Improving parametric mass modelling of lensing clusters through a perturbative approach

We present a new method to model the mass distribution of galaxy clusters that combines a parametric and a free-form approach to reconstruct cluster cores with strong lensing constraints. It aims at combining the advantages of both approaches, by keeping the robustness of the parametric component with an increased flexibility thanks to a free-form surface of B-spline functions. We demonstrate the capabilities of this new approach on the simulated cluster Hera, which has been used to evaluate lensing codes for the analysis of the Frontier Fields clusters. The method leads to better reproduction of the constraints, with an improvement by a factor $\sim3-4$ on the root-mean-square error on multiple-image positions, when compared to parametric-only approaches. The resulting models show a better accuracy in the reconstruction of the amplitude of the convergence field while conserving a high fidelity on other lensing observables already well reproduced. We make this method publicly available through its implementation in the Lenstool software.

astro-ph.CO↗

arXiv2020

An Atlas of MUSE Observations towards Twelve Massive Lensing Clusters

Spectroscopic surveys of massive galaxy clusters reveal the properties of faint background galaxies, thanks to the magnification provided by strong gravitational lensing. We present a systematic analysis of integral-field-spectroscopy observations of 12 massive clusters, conducted with the Multi Unit Spectroscopic Explorer (MUSE). All data were taken under very good seeing conditions (0.6") in effective exposure times between two and 15 hrs per pointing, for a total of 125 hrs. Our observations cover a total solid angle of ~23 arcmin$^2$ in the direction of clusters, many of which were previously studied by the MACS, Frontier Fields, GLASS and CLASH programs. The achieved emission line detection limit at 5$\sigma$ for a point source varies between (0.77--1.5)$\times$10$^{-18}$ erg\,s$^{-1}$\,cm$^{-2}$ at 7000\AA. We present our developed strategy to reduce these observational data, detect sources and determine their redshifts. We construct robust mass models for each cluster to further confirm our redshift measurements using strong-lensing constraints, and identify a total of 312 strongly lensed sources producing 939 multiple images. The final redshift catalogs contain more than 3300 robust redshifts, of which 40\% are for cluster members and $\sim$30\% for lensed Lyman-$\alpha$ emitters. 14\% of all sources are line emitters not seen in the available HST images, even at the depth of the FFs ($\sim29$ AB). We find that the magnification distribution of the lensed sources in the high-magnification regime ($\mu{=}$ 2--25) follows the theoretical expectation of $N(z)\propto\mu^{-2}$. The quality of this dataset, number of lensed sources, and number of strong-lensing constraints enables detailed studies of the physical properties of both the lensing cluster and the background galaxies. The full data products from this work are made available to the community. [abridged]

astro-ph.GA↗