Discovery of Strongly Lensed Quasars in the Ultraviolet Near Infrared Optical Northern Survey (UNIONS)

We report the discovery of five new doubly-imaged lensed quasars from the first 2 500 square degrees of the ongoing Canada-France Imaging Survey (CFIS), which is a component of the Ultraviolet Near Infrared Optical Northern Survey (UNIONS), selected from initial catalogues of either $Gaia$ pairs or MILLIQUAS quasars. We take advantage of the deep, 0.6 arcsec median-seeing $r$-band imaging of CFIS to confirm the presence of multiple point sources with similar colour of $u-r$, via convolution of the Laplacian of the point spread function. Requiring similar-colour point sources with flux ratios less than 2.5 mag in $r$-band, reduces the number of candidates from 256 314 to 7 815. After visual inspection we obtain 30 high-grade candidates, and prioritise spectroscopic follow-up for those showing signs of a lensing galaxy upon subtraction of the point sources. We obtain long-slit spectra for 18 candidates with ALFOSC on the 2.56-m Nordic Optical Telescope (NOT), confirming five new doubly lensed quasars with $1.21

Keywords:

• Nordic Optical Telescope
• Galaxy
• Astrophysics
• Point spread function
• Near-infrared spectroscopy
• Magnitude (astronomy)
• Quasar
• Redshift
• Spectral line
• Physics

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