A Tale of Two Wide Separation Gravitational Lenses

Abstract

<p>Wide separation gravitational lens systems are good candidates to probe the matter (luminous+dark) distribution in massive halos. Investigation of two wide separation lens systems is carried out. MG 2016+112 is a quadruply imaged lens system with a pair of merging partial images 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. New high resolution multi-frequency VLBI radio observations at 1.7, 5 and 8.4 GHz are carried out for MG 2016+112 to test previous mass models. The results from the new data are inconsistent with predictions of previous mass models. New mass models which quantitatively attribute the astrometric anomaly to a dwarf galaxy known at the redshift of the lensing galaxy, are presented. The level of substructure in MG 2016+112 is high compared to that suggested by CDM simulations of the sub-halo population. <br /> B2108+213, the widest separation lens system found in CLASS shows two lensed images and a third component in the radio whose identity was ambiguous. The lens galaxy G1 with a companion galaxy G2 belongs to a galaxy group. The new constraints from the high resolution VLBI observations are used to test various mass models. A profile steeper than isothermal is found to best fit the image positions and flux-density ratios. This might be due to interaction between G1 and G2 as suggested by numerical simulations. The third radio component is confirmed as the AGN of the massive lens galaxy G1 which is further supported by the extended emission from the radio lobes detected in the new MERLIN 1.4 GHz imaging.</p>