The faintest radio source yet: EVLA observations of the gravitational lens SDSS J1004+4112

TL;DR

This study reports the detection of the faintest radio source yet, using EVLA observations of a gravitational lens, demonstrating the potential of lensing to study nanoJy-level sources before the SKA era.

Contribution

First detection of an extremely faint radio source via gravitational lensing, showcasing EVLA's capability to probe nanoJy sources.

Findings

Detected four lensed images at 30-65 microJy

Estimated intrinsic flux density of about 2 microJy

Confirmed flux ratios consistent with optical observations

Abstract

We present new radio observations of the large-separation gravitationally-lensed quasar SDSS J1004+4112, taken in a total of 6 hours of observations with the Extended Very Large Array (EVLA). The maps reach a thermal noise level of approximately 7microJy. We detect four of the five lensed images at the 30-65microJy level, representing a source of intrinsic flux density, after allowing for lensing magnification, of about 2microJy, intrinsically probably the faintest radio source yet detected. This reinforces the utility of gravitational lensing in potentially allowing us to study nanoJy-level sources before the advent of the SKA. In an optical observation taken three months after the radio observation, image C is the brightest image, whereas the radio map shows flux density ratios consistent with previous optical observations. Future observations separated by a time delay will give the intrinsic flux ratios of the images in this source.