Modelling of the Complex CASSOWARY/SLUGS Gravitational Lenses

TL;DR

This paper presents high-resolution imaging and a novel inference approach to model the complex gravitational lens system CSWA 31, revealing detailed source and lens galaxy structures using advanced sampling techniques.

Contribution

It introduces a new prior distribution for multi-wavelength galaxy sources and applies Diffusive Nested Sampling for efficient inference in complex lens modeling.

Findings

Reconstructed the source as five merging spiral galaxies

Achieved a magnification factor of 13 for the source

Demonstrated the effectiveness of Diffusive Nested Sampling in lens modeling

Abstract

We present the first high-resolution images of CSWA 31, a gravitational lens system observed as part of the SLUGS (Sloan Lenses Unravelled by Gemini Studies) program. These systems exhibit complex image structure with the potential to strongly constrain the mass distribution of the massive lens galaxies, as well as the complex morphology of the sources. In this paper, we describe the strategy used to reconstruct the unlensed source profile and the lens galaxy mass profiles. We introduce a prior distribution over multi-wavelength sources that is realistic as a representation of our knowledge about the surface brightness profiles of galaxies and groups of galaxies. To carry out the inference computationally, we use Diffusive Nested Sampling, an efficient variant of Nested Sampling that uses Markov Chain Monte Carlo (MCMC) to sample the complex posterior distributions and compute the normalising constant. We demonstrate the efficacy of this approach with the reconstruction of the group-group gravitational lens system CSWA 31, finding the source to be composed of five merging spiral galaxies magnified by a factor of 13.