Pixel-level Modeling of Group-scale Strong Lens CASSOWARY 19

Abstract We present the first high-precision model for the group-scale strong lensing system CASSOWARY 19 (CSWA19), utilizing images from the Hubble Space Telescope. Sixteen member galaxies identified via the red-sequence method, and the main halo, all modeled as the dual Pseudo Isothermal Elliptical profile, are incorporated into a parametric lens model alongside an external shear field. To model the system, we adopt the PyAutoLens software package, employing a progressive search chain strategy for realizing the transition of source model from multiple Sérsic profiles to a brightness-adaptive pixelization, which uses 1000 pixels in the source plane to reconstruct the background source corresponding to 177,144 image pixels in the image plane. Our results indicate that the total mass within the Einstein radius is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>θ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">E</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> ≈ 1.41 × 10 13 M ⊙ and the average slope of the total mass density ρ ( r ) ∝ r − γ is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>γ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>˜</mml:mo> </mml:mrow> </mml:mover> <mml:mo>=</mml:mo> <mml:mn>1.33</mml:mn> </mml:math> within the effective radius. This slope is shallower than those measured in galaxies and groups but is closer to those of galaxy clusters. In addition, our approach successfully resolves the two merging galaxies in the background source and yields a total magnification of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>μ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>103.1</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.19</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.23</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , which is significantly higher than the outcomes from previous studies of CSWA19. In summary, our research demonstrates the effectiveness of the brightness-adaptive pixelization source reconstruction technique for modeling group-scale strong lensing systems. It can serve as a technical reference for future investigations into pixel-level modeling of the group- and cluster-scale strong lensing systems.