Deep radio observation of the gravitational lens candidate QSO2345+007

TL;DR

This study uses deep radio observations to investigate whether the double QSO2345+007 is a gravitational lens or a binary system, finding radio emission near one component but not the other, which is consistent with lensing.

Contribution

The paper provides the first deep radio imaging of QSO2345+007, offering new evidence to test the gravitational lens hypothesis versus a binary QSO scenario.

Findings

Detected radio emission near the brighter optical component

No significant radio detection of the second component

Radio flux ratio consistent with gravitational lens predictions

Abstract

The double QSO2345+007 comprises two optical components separated by 7.1\ arcseconds and is the most prominent `dark matter' gravitational lens candidate. Despite being known for more than a decade, optical spectroscopy and imaging have been unable to determine whether this double QSO is a binary QSO or a gravitational lens system. In this note we report a deep VLA observation of this system, yielding a map with a noise level of 8.5\ts $\mu$Jy per beam. We have a $4\sigma$ detection of a radio source within one arcsecond of the optical position of the brighter A-component of the QSO, but no significant detection of any radio counterpart of the B component. Given that the flux ratio in the optical waveband is $\sim$3--4, the gravitational lens hypothesis for this system would predict a radio flux of image B of $\lesssim 10$\ts $\mu$Jy. The non-detection of the B component is thus consistent with, but does not prove, the lens interpretation.