Mass Reconstruction of Galaxy-scale Strong Gravitational Lenses Using a Broken Power-law Model

TL;DR

This study evaluates the broken power-law (BPL) model's effectiveness in reconstructing galaxy-scale strong lensing masses using mock data, demonstrating its advantages over simpler models in accuracy and robustness.

Contribution

The paper provides an end-to-end assessment of the BPL model's performance in mass reconstruction, showing its superiority over single power-law models with robust bias metrics.

Findings

Einstein radius can be accurately determined with less than 1% bias.

BPL model achieves under 5% median bias within the Einstein radius.

BPL model estimates velocity dispersions with approximately 6% scatter.

Abstract

With mock strong gravitational lensing images, we investigate the performance of the broken power-law (BPL) model proposed by \citet{2020ApJ...892...62D} on the mass reconstruction of galaxy-scale lenses. An end-to-end test is carried out, including the creation of mock strong lensing images, the subtraction of lens light, and the reconstruction of lensed images, where the lenses are selected from the galaxies in the Illustris-1 simulation. We notice that, regardless of the adopted mass models (the BPL model or its special cases), the Einstein radius can be robustly determined from imaging data alone, and the median bias is typically less than $1\%$. Away from the Einstein radius, the lens mass distribution tends to be harder to measure, especially at radii where there are no lensed images detected. We find that, with rigid priors, the BPL model can clearly outperform the single power-law models by achieving $<5\%$ median bias on the radial convergence profile within the Einstein radius. As for the source light reconstructions, they are found to be sensitive to both lens light contamination and lens mass models, where the BPL model with rigid priors still performs best when there is no lens light contamination. We show that, by correcting for the projection effect, the BPL model can estimate the aperture and luminosity weighted line-of-sight velocity dispersions to an accuracy of $\sim6\%$ scatter. These results highlight the great potential of the BPL model in strong lensing related studies.