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

作者：Yu-Ching Chen, Arran C. Gross, Xin Liu, Yue Shen, Nadia L. Zakamska, Hsiang-Chih Hwang, Ming-Yang Zhuang · 发表于：The Astrophysical Journal · 年份：2025 · DOI：10.3847/1538-4357/ade23b · 被引用次数：6 · 研究领域：Galaxies: Formation, Evolution, Phenomena、Gamma-ray bursts and supernovae、Stellar, planetary, and galactic studies

Abstract 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.