Proper motion in lensed radio jets at redshift 3: a possible dual super-massive black hole system in the early Universe

TL;DR

This study uses gravitational lensing and VLBI radio observations to detect proper motion in a high-redshift lensed source, suggesting it may be a dual supermassive black hole system, providing insights into early Universe galaxy mergers.

Contribution

It presents the first evidence of proper motion in a gravitationally lensed radio source at high redshift, proposing a dual AGN scenario supported by multi-wavelength data.

Findings

Detected positional shifts up to 6 mas over 14.359 years.

Excludes lens galaxy shift, attributing motion to the background source.

Suggests the source may be a dual AGN system, the highest redshift known.

Abstract

In this paper, we exploit the gravitational lensing effect to detect proper motion in the highly magnified gravitationally lensed source MG B2016+112. We find positional shifts up to 6 mas in the lensed images by comparing two Very Long Baseline Interferometric (VLBI) radio observations at 1.7 GHz that are separated by 14.359 years, and provide an astrometric accuracy of the order of tens of $\mu$as. From lens modelling, we exclude a shift in the lensing galaxy as the cause of the positional change of the lensed images, and we assign it to the background source. The source consists of four sub-components separated by $\sim 175$ pc, with proper motion of the order of tens $\mu$as yr$^{-1}$ for the two components at highest magnification ($\mu\sim350$) and of the order of a few mas yr$^{-1}$ for the two components at lower magnification ($\mu\sim2$). We propose single AGN and dual AGN scenarios to explain the source plane. Although, the latter interpretation is supported by the archival multi-wavelength properties of the object. In this case, MG B2016+112 would represent the highest redshift dual radio-loud AGN system discovered thus far, and would support the merger interpretation for such systems. Also, given the low probability ($\sim10^{-5}$) of detecting a dual AGN system that is also gravitationally lensed, if confirmed, this would suggest that such dual AGN systems must be more abundant in the early Universe than currently thought.