Varstrometry for Off-nucleus and Dual Sub-Kpc AGN (VODKA): Long-slit Optical Spectroscopic Follow-up with Gemini/GMOS and Hubble Space Telescope/STIS

High spatial and spectral resolution observations are essential for identifying subarcsecond dual and lensed quasars and confirming their redshifts. We present Gemini/Gemini Multi-Object Spectrograph and Hubble Space Telescope/STIS optical spectra for 27 dual quasar candidates selected based on thei...

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Bibliographic Details
Published in:The Astrophysical journal Vol. 988; no. 1; pp. 126 - 136
Main Authors: Chen, Yu-Ching, Gross, Arran C., Liu, Xin, Shen, Yue, Zakamska, Nadia L., Hwang, Hsiang-Chih, Zhuang, Ming-Yang
Format: Journal Article
Language:English
Published: Philadelphia The American Astronomical Society 20.07.2025
IOP Publishing
Subjects:
Active galactic nuclei
Double quasars
Hubble Space Telescope
Quasars
Signal to noise ratio
Space telescopes
Spatial resolution
Spectral resolution
Spectroscopy
Strong gravitational lensing
Supermassive black holes
Vodka
ISSN:0004-637X, 1538-4357
Online Access:Get full text
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Summary:High spatial and spectral resolution observations are essential for identifying subarcsecond dual and lensed quasars and confirming their redshifts. We present Gemini/Gemini Multi-Object Spectrograph and Hubble Space Telescope/STIS optical spectra for 27 dual quasar candidates selected based on their variability-induced astrometric noise or double detections in Gaia (the Varstrometry for Off-nucleus and Dual sub-Kpc AGN (VODKA) project). From this follow-up, we spectroscopically identify 11 star superpositions and seven dual/lensed quasars. Among the remaining targets, two are likely dual/lensed quasars based on additional radio imaging, while the rest are quasars with unknown companions. Without prior photometric or spectroscopic selection, we find the star contamination rate to be 41%–67%, while the dual/lensed quasar fraction is ≳26% in the follow-up VODKA sample. However, when combined with existing unresolved spectra and spatially resolved two-band color cuts, the dual/lensed quasar fraction can be increased to ≳67%. Our study highlights the need for high-quality spectral data, including a signal-to-noise ratio of at least 20, spatial resolution that is at least twice finer than the source separation, and a spectral resolution of R  ≳ 1000, in order to separate close sources, exclude stellar superpositions, and reliably identify dual quasars.
Bibliography:Galaxies and Cosmology
AAS58366
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/ade23b