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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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ade23b |
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| author | Yu-Ching Chen Arran C. Gross Xin Liu Yue Shen Nadia L. Zakamska Hsiang-Chih Hwang Ming-Yang Zhuang |
| author_facet | Yu-Ching Chen Arran C. Gross Xin Liu Yue Shen Nadia L. Zakamska Hsiang-Chih Hwang Ming-Yang Zhuang |
| author_sort | Yu-Ching Chen |
| collection | DOAJ |
| description | 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. |
| format | Article |
| id | doaj-art-403700daf9754103b1d5665bfef4c3db |
| institution | DOAJ |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-403700daf9754103b1d5665bfef4c3db2025-08-20T03:12:46ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01988112610.3847/1538-4357/ade23bVarstrometry for Off-nucleus and Dual Sub-Kpc AGN (VODKA): Long-slit Optical Spectroscopic Follow-up with Gemini/GMOS and Hubble Space Telescope/STISYu-Ching Chen0https://orcid.org/0000-0002-9932-1298Arran C. Gross1https://orcid.org/0000-0001-7681-9213Xin Liu2https://orcid.org/0000-0003-0049-5210Yue Shen3https://orcid.org/0000-0003-1659-7035Nadia L. Zakamska4https://orcid.org/0000-0001-6100-6869Hsiang-Chih Hwang5https://orcid.org/0000-0003-4250-4437Ming-Yang Zhuang6https://orcid.org/0000-0001-5105-2837Department of Physics and Astronomy, Johns Hopkins University , Baltimore, MD 21218, USA ; ycchen@jhu.edu; Department of Astronomy, University of Illinois at Urbana-Champaign , Urbana, IL 61801, USA ; xinliuxl@illinois.eduDepartment of Astronomy, University of Illinois at Urbana-Champaign , Urbana, IL 61801, USA ; xinliuxl@illinois.eduDepartment of Astronomy, University of Illinois at Urbana-Champaign , Urbana, IL 61801, USA ; xinliuxl@illinois.edu; National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign , Urbana, IL 61801, USADepartment of Astronomy, University of Illinois at Urbana-Champaign , Urbana, IL 61801, USA ; xinliuxl@illinois.edu; National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign , Urbana, IL 61801, USADepartment of Physics and Astronomy, Johns Hopkins University , Baltimore, MD 21218, USA ; ycchen@jhu.eduSchool of Natural Sciences, Institute for Advanced Study , Princeton, 1 Einstein Drive, NJ 08540, USADepartment of Astronomy, University of Illinois at Urbana-Champaign , Urbana, IL 61801, USA ; xinliuxl@illinois.eduHigh 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.https://doi.org/10.3847/1538-4357/ade23bSpectroscopyStrong gravitational lensingDouble quasarsActive galactic nucleiSupermassive black holesQuasars |
| spellingShingle | Yu-Ching Chen Arran C. Gross Xin Liu Yue Shen Nadia L. Zakamska Hsiang-Chih Hwang Ming-Yang Zhuang Varstrometry for Off-nucleus and Dual Sub-Kpc AGN (VODKA): Long-slit Optical Spectroscopic Follow-up with Gemini/GMOS and Hubble Space Telescope/STIS The Astrophysical Journal Spectroscopy Strong gravitational lensing Double quasars Active galactic nuclei Supermassive black holes Quasars |
| title | Varstrometry for Off-nucleus and Dual Sub-Kpc AGN (VODKA): Long-slit Optical Spectroscopic Follow-up with Gemini/GMOS and Hubble Space Telescope/STIS |
| title_full | Varstrometry for Off-nucleus and Dual Sub-Kpc AGN (VODKA): Long-slit Optical Spectroscopic Follow-up with Gemini/GMOS and Hubble Space Telescope/STIS |
| title_fullStr | Varstrometry for Off-nucleus and Dual Sub-Kpc AGN (VODKA): Long-slit Optical Spectroscopic Follow-up with Gemini/GMOS and Hubble Space Telescope/STIS |
| title_full_unstemmed | Varstrometry for Off-nucleus and Dual Sub-Kpc AGN (VODKA): Long-slit Optical Spectroscopic Follow-up with Gemini/GMOS and Hubble Space Telescope/STIS |
| title_short | Varstrometry for Off-nucleus and Dual Sub-Kpc AGN (VODKA): Long-slit Optical Spectroscopic Follow-up with Gemini/GMOS and Hubble Space Telescope/STIS |
| title_sort | varstrometry for off nucleus and dual sub kpc agn vodka long slit optical spectroscopic follow up with gemini gmos and hubble space telescope stis |
| topic | Spectroscopy Strong gravitational lensing Double quasars Active galactic nuclei Supermassive black holes Quasars |
| url | https://doi.org/10.3847/1538-4357/ade23b |
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