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

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 µJy beam −1 (1𝜎). 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 ≥ 3 times the synthesized beam size, and the lensed images have a total flux density that is equivalent to at least a 20𝜎 (point-source) detection. For the ILT, this corresponds to a lens sample with Einstein radii ≥ 0.5 arcsec and a radio source population with 150 MHz flux densities ≥ 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.

DenseLens – Using DenseNet ensembles and information criteria for finding and rank-ordering strong gravitational lenses

“…Due to its success, CNNs have been applied to find strong lenses by Petrillo et al ( 2017Petrillo et al ( , 2019a, Pearson, Pennock & Robinson ( 2018 ), Davies, Serjeant & Bromley ( 2019 ), Metcalf et al ( 2019 ), Li et al ( 2020Li et al ( , 2021, and Rezaei et al ( 2022 ). In a recent strong gravitational lens finding challenge (Metcalf et al 2019 ), different machine learning algorithms and deep learning algorithms (such as SVM, ResNets, AlexNets) have been used.…”