Abstract
We present a new sample of galaxy-scale strong gravitational-lens candidates, selected from 904 square degrees of Data Release 4 of the Kilo-Degree Survey (KiDS), i.e., the "Lenses in the Kilo-Degree Survey" (LinKS) sample. We apply two Convolutional Neural Networks (ConvNets) to $\sim88\,000$ colour-magnitude selected luminous red galaxies yielding a list of 3500 strong-lens candidates. This list is further down-selected via human inspection. The resulting LinKS sample is composed of 1983 rank-ordered targets classified as "potential lens candidates" by at least one inspector. Of these, a high-grade subsample of 89 targets is identified with potential strong lenses by all inspectors. Additionally, we present a collection of another 200 strong lens candidates discovered serendipitously from various previous ConvNet runs. A straightforward application of our procedure to future Euclid or LSST data can select a sample of $\sim3000$ lens candidates with less than 10 per cent expected false positives and requiring minimal human intervention.
Highlights
Strong gravitational lenses1 are composite systems where a massive foreground object creates multiple images of one or more higher-redshift sources
This sample is comprised of a supersample of: (a) the same luminous red galaxies (LRGs) used for the lenses; (b) randomly selected galaxies from the survey with a r -band magnitude brighter than 21; (c) ‘false positives’ from earlier convolutional neural network (ConvNet); and (d) a sample of galaxies that were visually classified as spirals from an on-going GalaxyZoo project (Willett et al 2013, Kelvin et al, in prep.)
We present several samples of lens candidates from the Kilo-Degree Survey (KiDS) which likely contain several hundred strong gravitational lenses
Summary
Within the decade, ∼ 105 strong lenses are expected to be found in future surveys (Oguri & Marshall 2010; Pawase et al 2014; Collett 2015; McKean et al 2015) utilising, e.g., ESA’s Euclid mission (Laureijs et al 2011), the Large Synoptic Survey Telescope (LSST Science Collaboration et al 2009) and the Square Kilometer Array4 These surveys will allow lower-mass and higher-redshift lenses to be found, thanks to their deeper and higher angular resolution observations. We make use of the single-band and multi-band catalogues of the KiDS-DR4
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