A machine learning based approach to gravitational lens identification with the International LOFAR Telescope

TL;DR

This paper introduces a machine learning approach using convolutional neural networks to identify galaxy-scale gravitational lenses in interferometric radio data from the LOFAR Telescope, achieving high accuracy and low false positives.

Contribution

It develops and tests CNN models trained on simulated interferometric data to effectively detect gravitational lenses in LOFAR observations, with specific criteria for robust detection.

Findings

Recovered 95.3% of lensed samples with 0.008% false positives

Predicted sample purity of 92.2% for lensed events

Most robust detection when image separation > 3 times the beam size

Abstract

We present a novel machine learning based approach for detecting galaxy-scale gravitational lenses from interferometric data, specifically those taken with the International LOFAR Telescope (ILT), which is observing the northern radio sky at a frequency of 150 MHz, an angular resolution of 350 mas and a sensitivity of 90 uJy beam-1 (1 sigma). We develop and test several Convolutional Neural Networks to determine the probability and uncertainty of a given sample being classified as a lensed or non-lensed event. By training and testing on a simulated interferometric imaging data set that includes realistic lensed and non-lensed radio sources, we find that it is possible to recover 95.3 per cent of the lensed samples (true positive rate), with a contamination of just 0.008 per cent from non-lensed samples (false positive rate). Taking the expected lensing probability into account results in a predicted sample purity for lensed events of 92.2 per cent. We find that the network structure is most robust when the maximum image separation between the lensed images is greater than 3 times the synthesized beam size, and the lensed images have a total flux density that is equivalent to at least a 20 sigma (point-source) detection. For the ILT, this corresponds to a lens sample with Einstein radii greater than 0.5 arcsec and a radio source population with 150 MHz flux densities more than 2 mJy. By applying these criteria and our lens detection algorithm we expect to discover the vast majority of galaxy-scale gravitational lens systems contained within the LOFAR Two Metre Sky Survey.