Varstrometry for Off-nucleus and Dual Subkiloparsec Active Galactic Nuclei (VODKA): Investigating the Nature of SDSS J0823+2418 at z = 1.81, A Likely Lensed Quasar

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 and/or lensed quasar candidates discovered using astrometric jitter in Gaia data, we present a pilo...

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Published in:The Astrophysical journal Vol. 956; no. 2; pp. 117 - 136
Main Authors: Gross, Arran C., Chen, Yu-Ching, Foord, Adi, Liu, Xin, Shen, Yue, Oguri, Masamune, Goulding, Andy, Hwang, Hsiang-Chih, Zakamska, Nadia L., Ma, Yilun, Nolan, Liam
Format: Journal Article
Language:English
Published: Philadelphia The American Astronomical Society 01.10.2023
IOP Publishing
Subjects:
Active galactic nuclei
Astrophysics
Black holes
Coalescence
Double quasars
Galaxies
Galaxy mergers & collisions
Gravitational lensing
Near infrared radiation
Quasars
Sky surveys (astronomy)
Spectroscopy
Spectrum analysis
Supermassive black holes
Time lag
Vodka
X-ray astronomy
X-ray fluxes
ISSN:0004-637X, 1538-4357
Online Access:Get full text
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Summary: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 and/or 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 multiwavelength imaging and spectroscopy from X-ray to radio, we test whether the SDSS 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, near-IR (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 Sloan Digital Sky Survey spectra likewise suggest a foreground absorber via Mg ii absorption lines. We conclude that SDSS 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.
Bibliography:Galaxies and Cosmology
AAS47379
ObjectType-Article-1
SourceType-Scholarly Journals-1
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content type line 14
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/acf469