The role of luminous substructure in the gravitational lens system MG 2016+112

TL;DR

This study uses high-resolution VLBI observations to analyze gravitational lens MG 2016+112, revealing substructure, specifically a satellite galaxy, as the primary cause of observed astrometric anomalies, challenging some CDM predictions.

Contribution

The paper provides new high-resolution multi-frequency VLBI data and introduces refined mass models that identify a satellite galaxy as the main source of the lensing anomaly.

Findings

Detection of three new components in lensed images A and B.

Confirmation of opposite parity in images A and B.

Satellite galaxy's mass fraction exceeds CDM simulation predictions.

Abstract

MG 2016+112 is a quadruply imaged lens system with two complete images A and B and a pair of merging partial images in region C as seen in the radio. The merging images are found to violate the expected mirror symmetry. This indicates an astrometric anomaly which could only be of gravitational origin and could arise due to substructure in the environment or line-of-sight of the lens galaxy. We present new high resolution multi-frequency VLBI observations at 1.7, 5 and 8.4 GHz. Three new components are detected in the new VLBI imaging of both the lensed images A and B. The expected opposite parity of the lensed images A and B was confirmed due to the detection of non-collinear components. Furthermore, the observed properties of the newly detected components are inconsistent with the predictions of previous mass models. We present new scenarios for the background quasar which are consistent with the new observations. We also investigate the role of the satellite galaxy situated at the same redshift as the main lensing galaxy. Our new mass models demonstrate quantitatively that the satellite galaxy is the primary cause of the astrometric anomaly found in region C. The detected satellite is consistent with the abundance of subhaloes expected in the halo from cold dark matter (CDM) simulations. However, the fraction of the total halo mass in the satellite as computed from lens modeling is found to be higher than that predicted by CDM simulations.