Along the primary curve: Simultaneous source and lens reconstruction of bright arcs in cluster lenses

Pittsburgh Particle Physics, Astrophysics, and Cosmology Center (PITT PACC), Department of Physics and Astronomy, University of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260, USA

^⋆ Corresponding author: aa2@pitt.edu

Received: 24 October 2024
Accepted: 9 April 2025

Abstract

Context. Gravitational lensing is a phenomenon that arises when light rays are deflected by the mass between the source and the observer. Highly magnified and highly distorted images of background galaxies are formed by these angular deflections if the deflecting mass distribution and the background sources are aligned. As the most massive gravitationally bound objects in the universe, galaxy clusters are the prime location for such alignments. By carefully analyzing the images of lensed galaxies, we can measure the mass, both visible and invisible, along the line of sight. These measurements are crucial in investigating the nature of dark matter, which constitutes most of the mass within clusters.

Aims. Existing lensing analysis methods typically forward-model the multiple images of dozens of background galaxies lensed by the cluster. To make this forward-modeling computationally tractable, these multiple images are reduced to a much smaller summary data vector, which includes the locations, magnifications, and distortions. Our work avoids losing this information by forward-modeling the data at the pixel level.

Methods. We developed a parametric model for the angular deflections near the bright arcs, which allows us to control the shape of the curve. This curve indicates the directions of the eigenvectors of the Jacobian for the lensing matrix. Bright and extended images often follow such curves.

Results. We applied our analytical method to the bright arcs in gravitational lenses SDSS J1110+6459 and SDSS J0004−0103. Here, we present our lens and source reconstructions for each system. With future applications of our new method to many other lensing systems, we anticipate significant improvements in lens modeling near the critical curve, which will provide a higher level of precision for the mass reconstructions of the deflectors. High-precision lens models allow for more robust delensing, which is useful in studies of various highly magnified sources.