2025/04/08 by Yuanzhe Jiang, Jiang, Yuanzhe, Yue Shen +15 · 1 citation
Engineering · Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Space Technology and Applications
paper · pdf · doi:10.48550/arxiv.2504.06415
openalex publication_date 2025/04/08 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We preform a systematic search for galactic-scale quasar pairs and small-scale (<3 arcsec) lenses using the SDSS DR16 quasar catalog and Gaia DR3. Candidate double quasars (both are unobscured) are identified as Gaia resolved pairs around spectroscopically confirmed SDSS quasars (L\rm bol > 1044.5 \rm erg s-1) at 0.5 < z \lesssim 4.5. Gaia astrometric information and SDSS spectral decomposition are used to exclude foreground star superpositions, which dominate (\gtrsim 80% of) the pair sample. We identify 136 double quasar candidates from 1120 Gaia-resolved pairs after a magnitude and redshift cut of G<20.5 and z>0.5 (803 double quasars out of 2,497 pairs without any cuts applied) with separations of ∼ 0.3 - 3 arcsec, corresponding to projected physical separations of ∼ 3 - 30 kpc at the median redshift of the sample of z = 1.7. We estimate an overall double quasar (lens and physical pairs combined) fraction using this sample, corrected for pair-resolving completeness, of 5.7-0.3+0.3 × 10-4 (bootstrapping errors). This double quasar fraction increases toward smaller separations, consistent with earlier findings. We also find little redshift evolution of the double quasar fraction for the luminous SDSS sample, consistent with previous observations and simulation predictions. However, the observed fraction is lower than simulation predictions by ∼0.8 - 1.6 dex, suggesting a significant population of obscured quasar pairs are missed in our search. Future wide-area space missions targeting both unobscured and obscured quasar pairs at sub-arcsec resolutions will reveal this population of obscured quasar pairs, and extend to much lower AGN luminosities.