Role of the companion lensing galaxy in the CLASS gravitational lens B1152+199

TL;DR

This study reexamines the gravitational lens B1152+199 using HST and VLBI data, revealing the significant influence of the companion galaxy on the lensing effect and the importance of multi-wavelength modeling.

Contribution

It provides a detailed mass model of the dual-lens system, highlighting the role of the companion galaxy and demonstrating the consistency between radio and optical data.

Findings

The mass ratio between the host and X-galaxy is approximately 2.

The inner slope of the mass distribution is steeper than isothermal.

The diffuse emission in HST images is due to secondary lensing effects.

Abstract

We reinvestigate the Cosmic Lens All-Sky Survey (CLASS) gravitational lens B1152+199 using archived Hubble Space Telescope (HST) data and Very Long Baseline Interferometry (VLBI) data. A consistent luminosity ratio within effective radius between the host galaxy and the X-galaxy is measured from HST tri-band images, which leads to a mass ratio between the two galaxies as $r_b\sim 2$. To determine the role of the X-galaxy in the lens system, we modelled the dual-lens system with constraints from the VLBI-resolved jet components and the HST images. The 8.4-GHz global-VLBI data currently provide the most stringent constraints to the mass model, especially to the radial power-law slope. The optimized models for this two-image three-component radio lens favour a steeper-than-isothermal inner slope. The jet bending in image B was also investigated and it turned out to be rather a misalignment than a curvature. The goodness of fit indicates that the role of the X-galaxy is crucial in the lens system if three pairs of resolved jet components are to be fitted. When we imported the optimal model from radio constraints to optical modelling with the HST tri-band data, the optimization kept the consistency of the optimal model and successfully reproduced the features observed in the HST images. This implies that the diffuse emission discovered in the HST images is actually a detection of the secondary lensing effects from the companion lens.