GMP-selected dual and lensed AGNs: Selection function and classification based on near-IR colors and resolved spectra from VLT/ERIS, Keck/OSIRIS, and LBT/LUCI

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: filippo.mannucci@inaf.it
² Department of Physics and Astronomy, University of California Los Angeles, 430 Portola Plaza, Los Angeles, CA, 90095 USA
³ W. M. Keck Observatory, 65-1120 Mamalahoa Highway, Kamuela, HI, 96743 USA
⁴ Dipartimento di Fisica e Astronomia, Università di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy
⁵ Department of Physics, University of Arkansas, 226 Physics Building, 825 West Dickson Street, Fayetteville, AR, 72701 USA
⁶ Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
⁷ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
⁸ INAF – Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy
⁹ Physics and Astronomy Department “Augusto Righi”, Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
¹⁰ Institut d’Astrophysique de Paris, 98bis Bd Arago, 75014 Paris, France
¹¹ Large Binocular Telescope Observatory, Tucson, AZ, USA
¹² Max-Planck-Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
¹³ STFC UK ATC, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ UK
¹⁴ INAF – Osservatorio Astronomico d’Abruzzo, Via Mentore Maggini, 64100 Teramo, Italy
¹⁵ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁶ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
¹⁷ Leiden Observatory, University of Leiden, PO Box 9513 2300 RA Leiden, The Netherlands

Received: 13 May 2023
Accepted: 9 October 2023

Abstract

The Gaia Multipeak (GMP) technique can be used to identify large numbers of dual or lensed active galactic nucleus (AGN) candidates at subarcsec separation, allowing us to study both multiple supermassive black holes (SMBHs) in the same galaxy and rare, compact lensed systems. The observed samples can be used to test the predictions of the models of SMBH merging when (1) the selection function of the GMP technique is known, and (2) each system has been classified as a dual AGN, a lensed AGN, or an AGN/star alignment. Here we show that the GMP selection is very efficient for separations above 0.15″ when the secondary (fainter) object has a magnitude G ≲ 20.5. We present the spectroscopic classification of five GMP candidates using VLT/ERIS and Keck/OSIRIS and compare them with the classifications obtained from (a) the near-IR colors of seven systems obtained with LBT/LUCI, and (b) the analysis of the total spatially unresolved spectra. We conclude that colors and integrated spectra can already provide reliable classifications of many systems. Finally, we summarize the confirmed dual AGNs at z >  0.5 selected by the GMP technique, and compare this sample with other such systems from the literature, concluding that GMP can provide a large number of confirmed dual AGNs at separations below 7 kpc.