# SHARP - IV. An apparent flux ratio anomaly resolved by the edge-on disc in B0712+472

## TL;DR

This study demonstrates that the flux ratio anomaly in the B0712+472 lens system can be explained by the lens galaxy's edge-on disc, reducing the need to invoke dark matter substructures and emphasizing baryonic effects.

## Contribution

The paper introduces a detailed lens model including the galaxy's disc, showing it can account for flux anomalies without dark matter substructure assumptions.

## Key findings

- The disc accounts for 16% of the lensing mass within the Einstein radius.
- Inclusion of the disc explains flux anomalies without dark subhaloes.
- Highlights the importance of baryonic structures in lens modeling.

## Abstract

Flux ratio anomalies in quasar lenses can be attributed to dark matter substructure surrounding the lensing galaxy and, thus, used to constrain the substructure mass fraction. Previous applications of this approach infer a substructure abundance that potentially in tension with the predictions of a $\Lambda$CDM cosmology. However, the assumption that all flux ratio anomalies are due to substructure is a strong one, and alternative explanations have not been fully investigated. Here, we use new high-resolution near-IR Keck~II adaptive optics imaging for the lens system CLASS B0712+472 to perform pixel-based lens modelling for this system and, in combination with new VLBA radio observations, show that the inclusion of the disc in the lens model can explain the flux ratio anomalies without the need for dark matter substructures. The projected disc mass comprises 16% of the total lensing mass within the Einstein radius and the total disc mass is $1.79 \times 10^{10} M_{sun}$. The case of B0712+472 adds to the evidence that not all flux ratio anomalies are due to dark subhaloes, and highlights the importance of taking the effects of baryonic structures more fully into account in order to obtain an accurate measure of the substructure mass fraction.