2023/06/06 by Arran C. Gross, Gross, Arran C., Yu‐Ching Chen +19
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.48550/arxiv.2306.04041
openalex publication_date 2023/06/06 · openalex created_date 2023/06/09 · openalex updated_date 2026/08/01
Dual quasars at small physical separations are an important precursor phase of galaxy mergers, ultimately leading to the coalescence of the two supermassive black holes. Starting from a sample of dual/lensed quasar candidates discovered using astrometric jitter in Gaia data, we present a pilot case study of one of the most promising yet puzzling candidate dual quasars at cosmic noon (z∼1.8). Using multi-wavelength imaging and spectroscopy from X-ray to radio, we test whether the J0823+2418 system is two individual quasars in a bound pair at separation∼0.64'', or instead a single quasar being gravitationally lensed by a foreground galaxy. We find consistent flux ratios (∼1.25-1.45) between the two sources in optical, NIR, UV, and radio, and thus similar spectral energy distributions, suggesting a strong lensing scenario. However, differences in the radio spectral index, as well as changing X-ray fluxes, hint at either a dual quasar with otherwise nearly identical properties, or perhaps lensing-based time lag of ∼3 days paired with intrinsic variability. We find with lens mass modeling that the relative NIR positions and magnitudes of the two quasars and a marginally detected central galaxy are consistent with strong lensing. Archival SDSS spectra likewise suggest a foreground absorber via Mg II absorption lines. We conclude that J0823+2418 is likely a lensed quasar, and therefore that the VODKA sample contains a population of these lensed systems (perhaps as high as 50%) as well as dual quasars.