Gaia GraL: Gaia DR2 Gravitational Lens Systems. V. Doubly-imaged QSOs discovered from entropy and wavelets

A. Krone-Martins; M. J. Graham; D. Stern; S. G. Djorgovski; L. Delchambre; C. Ducourant; R. Teixeira; A. J. Drake; S. Scarano Jr.; J. Surdej; L. Galluccio; P. Jalan; O. Wertz; J. Klüter; F. Mignard; C. Spindola-Duarte; D. Dobie; E. Slezak; D. Sluse; T. Murphy; C. Boehm; A. M. Nierenberg; U. Bastian; J. Wambsganss; J. -F. LeCampion

arXiv · 1912.08977

Gaia GraL: Gaia DR2 Gravitational Lens Systems. V. Doubly-imaged QSOs discovered from entropy and wavelets

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Abstract

The discovery of multiply-imaged gravitationally lensed QSOs is fundamental to many astronomical and cosmological studies. However, these objects are rare and challenging to discover due to requirements of high-angular resolution astrometric, multiwavelength photometric and spectroscopic data. This has limited the number of known systems to a few hundred objects. We aim to reduce the constraints on angular resolution and discover multiply-imaged QSO candidates by using new candidate selection principles based on unresolved photometric time-series and ground-based images from public surveys. We selected candidates for multiply-imaged QSOs based on low levels of entropy computed from Catalina unresolved photometric time-series or Euclidean similarity to known lenses in a space defined by the wavelet power spectra of Pan-STARSS DR2 or DECaLS DR7 images, combined with multiple {\it Gaia} DR2 sources or large astrometric errors and supervised and unsupervised learning methods. We then confirmed spectroscopically some candidates with the Palomar Hale, Keck-I, and ESO/NTT telescopes. Here we report the discovery and confirmation of seven doubly-imaged QSOs and one likely double quasar. This demonstrates the potential of combining space-astrometry, even if unresolved, with low spatial-resolution photometric time-series and/or low-spatial resolution multi-band imaging to discover multiply-imaged lensed QSOs.

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A. Krone-Martins, M. J. Graham, D. Stern, S. G. Djorgovski, L. Delchambre, C. Ducourant, R. Teixeira, A. J. Drake, S. Scarano Jr., J. Surdej, L. Galluccio, P. Jalan, O. Wertz, J. Klüter, F. Mignard, C. Spindola-Duarte, D. Dobie, E. Slezak, D. Sluse, T. Murphy, C. Boehm, A. M. Nierenberg, U. Bastian, J. Wambsganss, J. -F. LeCampion. 2019-12-19. Gaia GraL: Gaia DR2 Gravitational Lens Systems. V. Doubly-imaged QSOs discovered from entropy and wavelets. https://arxiv.org/abs/1912.08977

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