Observations of radio-quiet quasars at 10mas resolution by use of gravitational lensing

TL;DR

This study uses gravitational lensing and radio observations to achieve 10-mas resolution of radio-quiet quasars, revealing detailed structures and flux characteristics that inform models of quasar radio emission.

Contribution

First high-resolution 10-mas radio imaging of a radio-quiet quasar, demonstrating the potential of gravitational lensing combined with VLA and e-MERLIN observations.

Findings

HS0810+2554 resolved, revealing a mini-AGN with a core and jet

Detected four faint radio sources, 1-5 μJy flux densities

Most lens models fit without requiring substructure, with some optical-radio flux anomalies

Abstract

We present VLA detections of radio emission in four four-image gravitational lens systems with quasar sources: HS0810+2554, RXJ0911+0511, HE0435$-$1223 and SDSSJ0924+0219, and e-MERLIN observations of two of the systems. The first three are detected at a high level of significance, and SDSS J0924+0219 is detected. HS0810+2554 is resolved, allowing us for the first time to achieve 10-mas resolution of the source frame in the structure of a radio quiet quasar. The others are unresolved or marginally resolved. All four objects are among the faintest radio sources yet detected, with intrinsic flux densities in the range 1-5$\mu$Jy; such radio objects, if unlensed, will only be observable routinely with the Square Kilometre Array. The observations of HS0810+2554, which is also detected with e-MERLIN, strongly suggest the presence of a mini-AGN, with a radio core and milliarcsecond scale jet. The flux densities of the lensed images in all but HE0435-1223 are consistent with smooth galaxy lens models without the requirement for smaller-scale substructure in the model, although some interesting anomalies are seen between optical and radio flux densities. These are probably due to microlensing effects in the optical.