VLT adaptive optics search for luminous substructures in the lens galaxy towards SDSS J0924+0219

TL;DR

This study uses high-resolution adaptive optics imaging to investigate luminous substructures in the lens galaxy of SDSS J0924+0219, finding no luminous substructure responsible for flux anomalies, suggesting microlensing and milli-lensing as explanations.

Contribution

The paper provides new high-resolution AO imaging data and analysis, showing that luminous substructures are unlikely to explain flux ratio anomalies in this lens system.

Findings

Object L is part of a bar in the lens galaxy, not responsible for flux anomalies.

No luminous substructure detected that explains flux ratio anomalies.

Flux ratio anomalies likely caused by microlensing and milli-lensing effects.

Abstract

Anomalous flux ratios between quasar images are suspected to be caused by substructures in lens galaxies. We present new deep and high resolution H and Ks imaging of the strongly lensed quasar SDSS J0924+0219 obtained using the ESO VLT with adaptive optics and the Laser Guide Star system. SDSS J0924+0219 is particularly interesting as the observed flux ratio between the quasar images vastly disagree with the predictions from smooth mass models. With our adaptive optics observations we find a luminous object, Object L, located ~0.3" to the North of the lens galaxy, but we show that it can not be responsible for the anomalous flux ratios. Object L as well as a luminous extension of the lens galaxy to the South are seen in the archival HST/ACS image in the F814W filter. This suggests that Object L is part of a bar in the lens galaxy, as also supported by the presence of a significant disk component in the light profile of the lens galaxy. Finally, we do not find evidence for any other luminous substructure that may explain the quasar images flux ratios. However, owe to the persistence of the flux ratio anomaly over time (~ 7 years) a combination of microlensing and milli-lensing is the favorite explanation for the observations.